Wherefore David blessed the Lord before all the congregation, and David said: “Blessed be You, Lord God of Israel our father, forever and ever… But who am I, and what is my people, that we should be able thus to offer willingly after this sort? for all things come of You, and of your own have we given You. For we are strangers before You, and sojourners, as were all our fathers: our days on the earth are as a shadow, and there is no abiding. O Lord our God, all this store that we have prepared to build You a house for Your holy name comes of Your hand, and is all Your own.” (I Divrei Ha-yamim 29:10-16)
"This is the offering which you shall take of them; gold, etc." R. Yehuda bar Simon said: The Holy One, blessed be He, said to Israel: Do not think that you are dealing bountifully with Me. The thirteen things that you set aside for Me correspond to the thirteen things that I did for you in Egypt, namely: “I clothed you with embroidered cloth, and shod you with tachash skin, and I girded you about with fine linen, and I covered you with silk. I decked you also with ornaments, and I put bracelets on your hands, and a chain on your neck, and I put a ring upon your nose, and earrings in your ears, and a beautiful crown upon your head" (Yechezkel 16:10-12). “My bread also which I gave you, fine flour, and oil and honey" (ibid. v. 19). These correspond to the thirteen things that you set aside for Me, and I regard it as if you were dealing bountifully with Me. David said: "I will sing to the Lord, because He has dealt bountifully with me" (Tehillim 13:6). And in the World-to-Come, I will repay you for these thirteen things: "And the Lord will create upon every dwelling place of Mount Zion, and upon her assemblies, a cloud and smoke by day, and the shining of a flaming fire by night; for upon all the glory shall there be a canopy. And from there shall be a tabernacle for a shadow in the daytime from the heat, and for a place of refuge, and for a covert from storm and from rain" (Yeshayahu 4:5-6). You repay Me, and I regard it as if you were dealing bountifully with Me. And [immediately] afterwards it is written: "Now will I sing to my well beloved" (Yeshayahu 5:1). This is: "I will sing to the Lord, because He has dealt bountifully with me." (Tanchuma Shemot 25:3)
Gold, Silver, & Copper
Likutei Sichot, vol. 6, pp. 157–160
.  Gold, silver, and copper: Although gold surpasses silver in its intrinsic value, silver is the metal of choice for use as currency. The very fact that silver is not as rare as gold makes it more suited for daily purposes, and in this respect it is more valuable than gold. Copper, on the other hand, is even more common than silver, but so much so that it lacks the distinction possessed by silver. (In the Torah, copper is not used as currency at all, and in societies where it is used for currency, it is typically used for coins of smaller denominations.)
Spiritually, the rarity of gold alludes to the otherworldly, transcendent element of man, the desire to rise above the natural and remain outside the common. Conversely, the currentness of silver alludes to the effort to draw otherworldly holiness into the common and mundane. Although gold is the more precious of the two metals, there are certain halachic contexts in which the currentness of silver makes it more valuable than gold.1 This advantage of silver over gold reflects the fact that it is the "silver" aspect of life that achieves the Divine plan.
Similarly, silver, gold, and copper represent the three types of Jews: Silver represents the perfectly righteous, who stand essentially above the mundane world and channel Divine enlightenment into it. Gold, in contrast, represents those of us who are initially thoroughly entrenched in the mundane world but have struggled with its spiritual darkness and won. Our initial situation impels us to seek transcendence and escape from the stranglehold of materialism. Copper, on the other hand, represents those of us who live within the mundane but bring no light into it. The Hebrew word for "copper" (nechoshet) comes from the word for "snake" (nachash). Copper is "snake-metal," a substance that recalls the stubborn impudence of the primordial snake's denial of God.
Nonetheless, the Torah requires that all three metals be used for the construction of the Tabernacle. This is a lesson both to those who perceive themselves as gold and silver as well as to those who think of themselves as copper. The righteous among us must not shy away from involvement in the physical world, preferring instead to occupy themselves with only spiritual matters. Neglecting to infuse materiality with spirituality could backfire: their necessary involvement in basic physical pursuits—such as food, clothing, and shelter—could drag them into the sensual experience of materiality and undermine their spiritual focus. Even the penitent among us, who are anyway engaged in a constant flight from materialism and therefore might feel immune to the danger posed by neglecting to infuse materiality with spirituality, are still not exempt from elevating the physical world. Finally, those of us whose penitence is far from complete might think that they have to first rectify and refine themselves before they can elevate the world, but the Torah tells them otherwise: they, too, must do their part in building God's home in this world.
Furthermore, the "gold" and "silver" Jews must realize that to merit the Divine presence they must unite with those on the level of copper.
Shimshon Raphael Hirsch
Looked at from this point of view, the materials which were to be donated for the building of the Mikdash-Mishkan indicate those of its qualities by means of which that "sanctity" is to be obtained, as well as this "dwelling," this proximity of God to us is proclaimed. For had we not first received these objects of our gifts from God? And in donating them to the sanctuary, do we not receive them back ourselves in doubly enhanced value, even as Yaakov expressed it when he laid the first foundation stone for the very first house of God, "And of that You shall give me I will surely give the tenth to You" (Bereishit 28:22). Or as David expressed it even more poignantly at the preparation for the building of the first Temple, "For all things come of You, and of your own have we given You" (I Divre Ha-yamim 29:14). Or what was brought here to us in still more comprehensive brevity in the throwing of half of the blood of the covenant towards the altar and half towards the people.
In our discussion in Jeshurun (V, p. 232ff.), we have proved that in Scripture, metals in general, in accordance with their physical property of hardness, are used as a metaphor for firmness and strength (e.g., Yirmiyahu 1:15, Iyov 6:12, Yeshayahu 48:4), and in accordance with their being valuable, as a metaphor for valuing spiritual values (e.g., Mishlei 2:10,Tehillim 19:11, Iyov 28), but quite specially in accordance with their metallurgical properties as the most suitable metaphor for all goodness and truth in every stage of admixture with evil and the untrue, and also for the processes of tests and purifying and refining applied to morality and truth (e.g., Iyov 23:10, Zekharya 13:9, Malakhi 3:3, Yeshayahu48:10, Mishlei 25:4, 10, 20 and 36:23, Yirmiyahu 6:29-30, Tehillim 99:119; Yechezkel 22:18, Yeshayahu 1:22; Daniel 2:32- 33). In all these places, metals are used to designate the various degrees of moral purity and truth. Whereas copper represents an ignoble nature, one not yet refined; silver describes the stage of still requiring purification, but of being able and fit to be refined; gold, which is usually found pure, and unmixed, and also resists the strongest tests, is the picture of the purest, most sterling, moral nobility and of true, real permanence and constancy.
Metals combine the highest degree of adaptiveness with the highest degree of firmness and stability; under heat and hammer, they can be adapted to any desired form, but once they have received that form, they retain it with a persistence that can only be destroyed by violence. They represent by these properties just those very characteristics that we should have towards our duty in general, and especially towards the will of God, as revealed to us by His word. His word is described too as "Hammer" and "Fire" (Yirmiyahu 23:29). So that metals offer themselves more than anything else for allegorical expressions of our moral relations to our calling.
So that, according to their metallurgical characteristics, copper would represent the ignoble nature, silver, the one who is ready to be ennobled by purification, gold, the original and test-resisting, the most complete purity and goodness…
From all these verses, it follows that the metals symbolize the purity of morality and truth at different levels. Brass, iron, and all the non-noble metals symbolize non-refined nature, which has not yet reached the level of nobility. Whereas silver and gold symbolize the levels of the purity of moral nobility, of true fidelity to one's faith, as the Holy One, blessed be He demands of us, according to His holy will. (ibid.)
The offerings to the Mishkan correspond to the heavenly beings: Gold – this is the sun; silver – this is the moon; brass – this is the west. When the sun sets, the face of the west looks like brass. Blue – this is the firmament; purple – this is the clouds; scarlet – this is the rainbow; and linen – this is the serafim… For the Holy One, blessed be He, said: Just as my dwelling is in heaven, if you make Me a sanctuary on earth, I will dwell in it, as it says: "And let them make Me a sanctuary, that I may dwell among them" (Shemot 25:8). (Midrash Ha-Gadol, Shemot, Parashat Teruma 5)
The offerings to the Mishkan correspond to man's body: Gold – this is the soul; silver – this is the body; … Blue – this is tendons; purple – this is flesh; scarlet – this is the blood. The Holy One, blessed be He, said: When I examine them and find them complete and perfect, I dwell among them, as it says: "And let them make Me a sanctuary, that I may dwell among them" (Shemot 25:8). (Midrash Ha-Gadol, Shemot, Parashat Teruma 4)
The Ramban, (in his discussion of the mitzva of tzitzit,)
Rather, the remembrance [of the commandments] is through the blue thread, which alludes to the all-inclusive attribute, which is ba-kol, and which is the aim of all. Therefore, he said, "That you may look upon it, and remember kol (all)," which is the commandments of God. This is what the Rabbis said: [Why was blue chosen rather than any other color?] Because blue resembles the sea, and the sea resembles heaven, and heaven resembles the Throne of Glory, etc. The likeness is in the name, as also in the shade of the color, which is the termination of all colors [and which leads one from the blue in the fringes to the blue of the sea, etc., and finally to think of Him who is on high], for in the distance all colors appear to be that shade. That is why it is called tekhelet. (Commentary to Bamidbar 15:38)
This teaches you that blue resembles [the color of] the sea, and the sea resembles [the color of] the grass, and the grass resembles [the color of] heaven, and heaven resembles [the color of] the Throne of Glory, as it is written, "Then I looked, and behold, in the firmament that was above the head of the keruvim there appeared over them something like a sapphire stone, like what appeared to be the shape of a throne" (Yechezkel 10:1). (Yerushalmi Berakhot 1:3)
Because blue resembles [the color of] the sea, and the sea resembles [the color of] heaven, and heaven resembles [the color of] the Throne of Glory, as it is said, "And they saw the God of Israel and there was under His feet as it were a paved work of sapphire stone, and as it were the very heaven for clearness" (Shemot 24:10), and it is written, "The likeness of a throne as the appearance of a sapphire stone" (Yechezkel 1:26). (Sota 17a)
midrash Mishnat Rabbi Eliezer (chap. 14) and in Midrash Ha-Gadol (end of Parashat Shelach),
R. Yehuda the son of R. El'ai says: Why was the Torah strict about blue? Because blue resembles [the color of] sapphire, and the staff of God was of sapphire. This teaches you that whenever Israel would look at this blue, they would remember all those signs and wonders that the Holy One, blessed be He, performed by way of that staff, etc.
And the Sages say: Why was the Torah strict about blue? Because blue resembles [the color of] sapphire, and the tablets [of the law] were of sapphire. This teaches you that whenever Israel would look at this blue, they would remember what was written in the tablets, and observe them. And similarly it says: "And it shall be to you as a fringe, that you may look upon it and remember" (Bamidbar 15:39).
The ark is dear like the heavenly Throne of Glory… Even when they journeyed, they would not spread over it a cloth of purple or a cloth of scarlet, but only a cloth wholly of blue. Why? Because blue resembles [the color of] the sea, and the sea resembles [the color of] heaven, and heaven resembles [the color of] the Throne of Glory… This teaches you that the ark resembled the Throne of Glory. And therefore it says regarding it: "Wholly of blue" – that all of it resembled it. And since the ark was similar to it, therefore the cloth was on top – facing heaven, which was similar to it, which you do not find regarding the other vessels… And furthermore, regarding the ark it says: "Wholly of blue," which is not stated regarding all of them. Why "wholly of blue"? Because it is the most important of all the vessels of the Mishkan.
Because of the importance of the ark, the covering of tachash skin was not visible [at all] upon it, for they covered [the ark firstly] with the parokhet as a screening partition, and then they covered both of them [the ark and the parokhet] with the covering of the tachash skin [as a protection] against the rains, and above them all they spread a cloth all of blue, so that this distinguished garment, which was the like of the very heaven for clearness, should be seen upon it. But as for all the other vessels – the table, the candlestick, and the altars – the covering of the tachash skin was visible over them. (Commentary to Bamidbar 4:6)
They said: He who has not seen the Temple of Herod has never seen a beautiful building. Of what did he build it? Rabba said: Of yellow and white marble. Some say, of blue, yellow and white marble. Alternate rows [of the stones] projected, so as to leave a place for cement. He originally intended to cover it with gold, but the Rabbis advised him not to, since it was more beautiful as it was, looking like the waves of the sea. (Bava Batra 4b)
Shimshon Raphael Hirsch
Even one who disagrees with our understanding of the symbolism of the colors would certainly agree with us that blue is the fundamental color of the Mikdash and of the High Priest's garments, and that blue symbolizes heaven and that which Israel received from heaven. As Chazal said: "How is blue different from all the colors? Because blue resembles the sea, and the sea resembles heaven, and heaven resembles the Throne of Glory, as it is stated: ‘And there was under His feet as it were a paved work of sapphire stone, and as it were the very heaven for clearness’ (Shemot 24:10). And it is written: ‘The likeness of a throne as the appearance of a sapphire stone’ (Yechezkel 1:26)’ (Menachot 43b). Accordingly, no other color than blue is capable of symbolizing the special relationship between God and Israel. The thread of blue in our garments symbolizes that we play the role of a High Priest on earth, and it symbolizes "And you shall be holy men to Me" (Shemot 22:30), and it symbolizes
“Ve-tola'at shani” – Wool that is dyed red is called tola'at, and the color is called shani. As it is written: "The valiant men metula'im" (Nachum 2:4), which means: wearing garments that are dyed [red]. And similarly: "They that were brought up in tola" (Eikha 4:5), which means: in dyed garments. This is also proven by the verse: "Though your sins be like shanim, they shall be as white as sheleg; though they be red like tola, they shall be white as tzemer." Shani and sheleg are dyes, one red and the other white. But tola and tzemer are both wool; tola is dyed wool, and tzemer is white, without dye. (Commentary to Shemot 25:4)
"They shall be like wool" – My father, of blessed memory, explained: If your sins be like shanim – which is not a deep red - they shall be as white as snow – I shall atone for your sins. If they be very red like tola, they shall be white as wool, which is not as white as snow. (Commentary to Yeshayahu 1:18)
The table corresponds to the kingdom of the house of David. The table is covered with blue, corresponding to David, who was a righteous man, and the Holy One, blessed be He, made a covenant of kingdom with him, for him and his sons. He therefore separated its vessels from it and covered them with scarlet, for because of the sins of his sons, the kingdom was divided. And therefore it and its vessels had a single covering, because in the end, the kingdom will return to them as at first. (Bamidbar Rabba 4:14)
The Maharal of Prague netzach Yisra'el (ch. 31):
The color white is absolute simplicity, for the color white is not called a color, for this color has absolute simplicity.
Netiv Ha-Torah (ch. 10),
The Holy of Holies, owing to its holiness, was totally removed from this material world, and therefore he was only permitted to enter the Holy of Holies wearing white garments.
I pray You, let me go over and see the good land that is beyond the Jordan, that goodly mountain region and the Lebanon (Levanon)" (Devarim 3:25), Rashi writes: "And the Lebanon – this is the Temple."
R. Shimon ben Yochai taught: Why is it called Lebanon? Because it whitens the sins of Israel like snow. This is what the verse states: "Though your sins be like scarlet, they shall be as white as snow; though they be red like crimson, they shall be white as wool" (Yeshayahu 1:18). (Vayikra Rabba 1:2).
"Come with me from Lebanon, my bride, with me from Lebanon" (Shir Ha-shirim 4:8). What is Lebanon? This is the Temple, which is called Lebanon. And why is it called Lebanon? Rather, anyone who went up there with a sin in his hand would not leave there until his sins were whitened like snow, to fulfill what is stated: "Though your sins be like scarlet, they shall be as white as snow." (Midrash Zuta on Shir Ha-shirim 4:8)
From where do we know that a crimson-colored strap is tied to the head of the goat that is sent to Azazel? Because it says: “Though your sins be like scarlet, they shall be as white as snow." (Shabbat 86a)
Rabbenu Bachayei explains in his commentary to the mitzva of tzitzit:
"And they shall make themselves fringes" (Bamidbar 15:38)… And we were commanded to wrap ourselves in it, from that which we expounded (Rosh Ha-Shana 17b): "'And the Lord passed by before him and proclaimed.' Were it not written in the text, it would be impossible for us to say such a thing. This verse teaches us that the Holy One, blessed be He, wrapped Himself in a tallit like a prayer leader and showed Moshe the order of prayer. He said to him: Whenever Israel sin, let them carry out this service before Me, and I will forgive them." What this statement means is that [God] came to teach us the order of prayer and supplication, how we should plead before Him, and that He wrapped Himself in a tallit, and that we should mention before Him the thirteen attributes [of Mercy] with [full] concentration, and He will pardon us. And when it says: "He wrapped Himself," it means in a white tallit, which is a sign of forgiveness and atonement. Just like the color red is a sign of sin, so whiteness is a sign of pardon. This is what it says: "Though your sins be like scarlet, they shall be as white as snow; though they be red like crimson, they shall be white as wool" (Yeshayahu 1:18). (Bamidbar 15:38
The thread of linen was white. The garments made of linen were called "the white garments" (Yoma 9a). The color white describes in all places, according to human understanding, purity, as it is written: "Let your garments be always white" (Kohelet 9:8). This color symbolizes both physical and moral purity, as it is written: "Purge me with hyssop, and I shall be clean: wash me, and I shall be whiter than snow" (Tehillim 51:9). Similarly: "Though your sins be like scarlet, they shall be as white as snow" (Yeshayahu 1:18). The process of purification is itself called "whitening," as it is written: "Many shall purify themselves and make themselves white and be tried" (Daniel 12:10). We must therefore understand that the color white of the linen is a symbol of purity, of plant-like purity. The statutes relating to moral purity are very prominent in the Torah; they demand that one restrain natural life, passions and lusts, that one distance oneself from sexual corruption and from the desecration of life. These are the conditions without which it is impossible to arrive at spiritual perfection and moral closeness to God. Thus, it is evident that the color white of the linen symbolizes purity. Purity is that level of nobility demanded by the Torah… The color white as a symbol of cleanness and purity is expressed also in the following verses: "If I wash myself with snow water, and make my hands never so clean" (Iyov 9:30), and "Her Nazirites were purer than snow; they were whiter than milk" (Eikha 4:7).
We have already spoken about linen. The next level is scarlet, and above that purple. Both of these are reds, and so these are merely two shades of the same level. Both are wool, and the color of both shades is derived from a living creature… Having seen that linen symbolizes the vegetative dimension, we can now say that the three shades of wool symbolize the life of that which has an animated spirit.
The color red is mentioned in the Bible in various places, and it symbolizes animated life. As in: "And he sent, and brought him in. Now he was ruddy (admoni), with fine eyes, and good looking" (I Shmuel 16:12). Here, the color symbolizes health and physical perfection. Esav was also born red: "And the first one came out red, all over like a hairy garment" (Bereishit25:25), "therefore was his name called Edom (red)" (ibid. v. 30). "Her Nazirites were purer than snow, they were whiter than milk, they were more ruddy in body than rubies" (Eikha4:7); "My beloved is white and ruddy" (Shir Ha-shirim 5:10). This means: pure and full of animated life. The color red also symbolizes blood, as it is written: "Your hands are full of blood" (Yeshayahu 1:15); "Why is your apparel red" (ibid. 63:2); "The shield of the mighty men is made red, the valiant men are in scarlet" (Nachum 2:4). But blood symbolizes not only sin, but also that which bears the force of life: "For the life of all flesh is its blood, on which its life depends" (Vayikra 17:14).
Accordingly, wool symbolizes the fleshly-beastly dimension of human life, and when the wool is red, it symbolizes healthy and animated life. This life is at two levels: purple and scarlet. The Torah lists the materials of which the priestly garments were fashioned in the order of their importance, from the most important to the least important, with all the intermediate levels. Therefore, scarlet appears below the level of purple. We see this in all the verses which mention these colors, e.g., in the verses speaking of the clothing of officers and rulers: "Blue and purple is their clothing, they are all the work of skillful men" (Yirmiyahu 10:9); "Besides the crescents, and the eardrops, and the purple garments that were on the kings of Midyan" (Shoftim 8:26). So too: "And Mordekhai went out from eh presence of the king in royal apparel of blue and white, and with a great crown of gold, and with a wrap of fine linen and purple" (Esther 8:15), and so too: "She makes herself coverlets; her clothing is fine linen and purple" (Mishlei 31:22), but "For all her household are clothed with scarlet" (ibid. v. 21).
The color scarlet is a simple color, as in: "And You, O ruined one, what will you do? Though you clothe yourself with scarlet, though you deck yourself with ornaments of gold, though you enlarge your eyes with paint, in vain shall you make yourself fair; your lovers will despise you, they will seek your life" (Yirmiyahu 4:30). So too: "They that were brought up in scarlet embrace dunghills" (Eikha 4:5).
In this way, life is described at a lower level and at a higher level. The difference seems to be as follows: First, the bodily forces that man shares with all living creatures, and afterwards the forces that are fit for man. Man (adam) is called by that name because of the color red (adom). We already wrote in our discussion of tzitzit that the color red is the color whose light is broken least of all the colors, and therefore this color is most appropriate for man, he being the creature who is closest to God, having been created in the image of God, as it is written: "Yet You have made him a little lower than the angels" (Tehillim 8:6).
Regarding blue, we have already said that it is the color that is seen on the horizon and that it covers that which is not seen, the Divine dimension of creation. Accordingly, we said that the blue thread on a garment points to the Divine dimension of the covenant between God and man. It is the symbol of the pure man who connects with the Divine dimension in every aspect of his life.
Thus, we have four colors and materials:
Linen, which represents the vegetative dimension.
Scarlet, which represents the animated dimension.
Purple, which represents the human dimension.
Blue, which represents the Divine dimension.
All the colors are found in man's essence and in his relationship with God.
He who looks will find that everything about the Mishkan was modeled after natural things… He will see that the Mishkan, which was thirty cubits long, was divided into three parts. Into the first two outer parts the priests were granted permission to enter. They allude to the sea and the land, which are places through which people move. The other part of the Mishkan, which is the Holy of Holies, alludes to heaven, through which no man's foot passes…
Later in his discussion, the Abarbanel relates to the issue of the colors, saying as follows:
As all the hangings have four colors, they allude to the four fundamental elements, namely:
The linen alludes to the earth, as flax grows from it.
The purple resembles blood, as it is made from the blood of a particular fish.
The blue alludes to the air.
The scarlet alludes to fire.
The priestly garment, which was of linen, alludes to the entirety of the earth.
The pomegranates allude to lightening and the heavenly lights, and the sound coming from the pomegranates alludes to all the natural things.
For this reason, God commanded that it be woven from the four colors mixed with gold, alluding in my opinion to the light that is scattered in the world…
Wool & Linen
You shall keep My statutes. You shall not let your cattle gender with a diverse kind; you shall not you sow your field with mingled seed: neither shall a garment mingled of linen and wool come upon you. (Vayikra 19:19)
And the reason for kil'ayim is that God created the different species in the world for all the different kinds of souls, in plants and in those that have the animative soul, and he gave them the power of reproduction, that the species should exist for eternity, for as long as He should desire the existence of the world, and He ordered that that power should reproduce the species and never ever change, as is written concerning each (species), "le-mineihu" (for its species)… But one who intermixes two species changes and negates the act of creation, as though he thinks that God did not complete His world sufficiently, and he wishes to assist creation by adding creatures to it. (Vayikra 11:19)
There are three different types of forbidden mixtures dealt with here, which can be categorized into two classes. While there are certain instances where clothing may contain a combination of wool and linen, such as the garments worn by the priests in the Holy Temple and a garment bearing tzitzit, the crossbreeding of both animals and plants is never allowed.
This may be understood in light of the differences between the two. The prohibition against combining fibers is a seemingly illogical law. After all, even after they are woven together the fibers remain two separate entities; it is possible to completely unravel and reverse the combination.
Crossbreeding, on the other hand, is a readily understandable law. G‑dcreated many different species, and commanded them to remain pure and true to their nature. By tampering with them, man is disturbing the order of Creation and causing a different, new, and confused entity to come into being. The product cannot be considered the result of either of its two antecedents, but rather a brand new entity. Regardless of when or where, this is something that can never be allowed.
Why, then, can fibers indeed not be combined, and why is an exception made for the priestly garments and tzitzit?
Rabbeinu Bachya explains the Kabbalistic secret of shatnez, the prohibition of combining wool and linen, as follows:
When one mixes two incompatible species, this causes friction, for he is jumbling the supernal energies and changing them from their proper state…. The two firstborn of the world [Cain and Abel] were such a mixture, one good and one bad. We are enjoined to follow only the spirit of holiness and to distance ourselves from that which is evil and impure. This is why such forbidden mixtures are forbidden, for they fuse the two opposite extremes, and their combinations do not work well…
Of the two firstborn, one [Cain] brought flax [linen] as his sacrifice, while the other [Abel] brought wool [sheep]. Therefore, we may not wear a mixture of wool and linen, for one who wears such a combination jumbles the spiritual energies…. Jews are forbidden to wear this combination of opposites in order to stay away from the spirit of impurity and in order to become sanctified with the spirit of holiness.
Avoiding any influence of that which is impure, implies that there is no problem with the mixture per se, but rather that by combining these two species the holy is being tainted by the impure. The problem is in the fact that they are being combined, even if there is no problem with either of the two components. Each one is a different species, and it is unnatural for the two to be mixed. In spiritual terms, this causes a merger of different energies, which results in one or the other being perverted from its proper mission.
Although all spiritual energies are supposed to coexist and overlap, that is only as long as neither lose their identity altogether. Cooperation is fine - losing oneself in another's identity is not. This can be compared to the way a king desires his ministers to behave. He wants them to work so well together that their different portfolios integrate seamlessly. Nevertheless, each one has his/her own specific mission, which is distinct from that of every other one. If these separations are lost, the king will definitely not be pleased.
This is true, however, only when the ministers are functioning independently of the king. When they are in the presence of the king, they lose all sense of self, for they are totally nullified before the over-powering essence of their master. Here, any demonstration of self-assertion would be out of place and an affront to the king's majesty. As they bow before him, there are indeed no differences between the ministers, and even those that are total opposites become one.
So it was in the Holy Temple. In the face of its holiness, the impurities inherent in the flax could not exist, and so its presence would not sully the purity of the wool. And, because of the intense degree of spirituality manifest while the priests served G‑d there, even diverse, contrary energies were peacefully joined.
In fact, this is the root of the difference of opinions between two early great Torah authorities as to when this exception applies. Rambam maintains that the priests could only wear the priestly garments in the Temple while actively involved in the priestly service. Ra'avad, however, disagrees, saying that they could wear them at all times, as long as they were on the Temple premises.
Ra'avad considers the prohibition against shatnez to be because of the evil of the flax. Since evil has no place in the Temple, there is no problem at all with shatnez in those holy confines, even when one is not involved in actual service.
Rambam disagrees, viewing the convergence of disparate energies as being the main issue, resulting in the prohibition against shatnez. Even while in the Temple, these energies are present and retain their differences. It is only while directly involved in the divine service that G‑d's overpowering Oneness is manifest, and all distinctions lose their meaning. It is only then, therefore, that the combination of wool and linen may be worn.
[from Likutei Sichot, vol. 29, pp. 122-9, vol. 36, pp. 155-7]
Shimshon Raphael Hirsch a-Mitzvot Ki-Semalim
We see that the prohibition has various reasons: Man is not to intervene in the created world in a manner that will change the laws of nature in an arbitrary manner. One must respect the laws of the Creator that He gave to His creatures, and one must also keep the laws of nature and everything that depends upon them, in sanctity and in purity, and one must especially preserve the existence of the creatures. If we delve just a bit into these laws, we will understand their reasons. Surely, the grafting of trees of different species and the mating of animals of different species constitutes interference in creation on the part of man, in an unnatural manner. Natural forces and seeds would become joined and mingled, and forces foreign to each other would be mixed up by force, things that would never have become mixed freely on their own. These forces are separated and distinguished one from the other…
These laws were given so that every plant, even the most modest, would develop without change, and thus demonstrate its obedience to the Creator, to the point that the fields and gardens of the Holy Land continuously bring to mind He who established the law and order of the world. All creatures develop exclusively in accordance with the great principle of creation, "after its kind," and according to its understanding it freely recognizes its obligation, understands it, and fulfills its commandments. This warning is found wherever man goes: in the field, in the raising of livestock, in working with animals, in his food, when he eats of cattle or fowl, and also in his clothing he recognizes the great principle in accordance with which nature was created. To the extent that the organic materials of nature serve man, care must be taken that this use should not involve a contradiction to the laws of nature.
Now we shall consider the prohibition of sha'atnez, using wool and linen together.
This prohibition does not apply in general to the mixture of different materials in the fashioning of fabrics, but only to wool and linen. Accordingly, the intent of the prohibition is not to remind us of the great order that the Holy One, blessed be He, implanted in His world in general, but rather that this mixture stands in special connection to this preeminent law of nature. It is assigned a special role within this law for man…
Man is distinguished from animals also by way of his clothing, by way of his external appearance that expresses itself in the covering of his body, and in particular we see the intention underlying the prohibition of sha'atnez, when we see the special relationship between this prohibition and the mitzva of tzitzit.
When we examine the intention of the prohibition of sha'atnez, we must keep in mind man's purpose in general, because of which he is man, and the mixing of the two species was liable to bring man down to the level of animals. Therefore, there are two factors that distinguish man from animal, both concealed in the body, which man presents only when it is covered in clothing, and he also covers himself with it in order to protect himself from outside influences. The goals of clothing are symbolized by the tzitzit.
Wool and linen are not two types of the same species; they do not grow in the same area. The relationship between them is like the relationship between plant and animal. Linen is the typical material worn from the plant kingdom, and wool from the animal kingdom. Accordingly, it would have been possible to assume that a person's clothing made of wool and linen symbolizes the relationships between man's body and the plant and animal kingdoms.
Surely, man's body is comprised of these two factors, the plant and the animal. Alimentation and reproduction and all that stems from them belong to vegetative part of his body, while feeling, will, and movement belong to the fleshly part of the essence of man's body. In animals, the fleshly part is subject to the vegetative part – will, movement and reproduction serve alimentation. The two factors are mingled one with the other; both of them constitute the essence of the animal, a creature that has but alimentation, reproduction, movement, and will. An animal has wool that serves the linen, "wool and linen together."
Man, however, has a higher destiny. His vegetative dimension does not rule over his fleshly part. The fleshly part serves the vegetative, but the two of them serve the image of God in man, the Divine dimension, which is the third factor, and it alone turns man into a creature worthy of that name. Man does not want his senses exclusively for alimentation and reproduction, but rather he nourishes himself and reproduces in order to place his will and actions at God's disposal.
Three levels complete creation: plant, animal and man; and above all of them stands God. Plant and animal are intermingled in animals. The rule of the fleshly over the vegetative part, and the subjugation of the two of them to God and His holy will is called "sanctification," as in: "And you shall sanctify yourselves and be holy" (Vayikra 11:44)…
We therefore assume that the prohibition of sha'atnez symbolizes for us the severe warning that we not allow man's fleshly nature to descend to the area of vegetative stimuli that intermingle with the fleshly part and subjugate the body. Just the opposite: the vegetative part of the body should bear our fleshly life, and that should bear the image of God, the Divine dimension on earth, so that man should be worthy of that description. Here we see the same warning that Chazal issue elsewhere: "His heart sees his nakedness" (Berakhot25b).
Man's nakedness symbolizes the animal dimension of his life in a most demonstrable manner, and the heart is directed upwards towards holiness. Therefore, a person is forbidden to occupy himself in holy matters, such as a blessing, as long as there is no separation between heart and nakedness. It is in this sense that Chazal explain the concept of sha'atnez. They say: "R. Shimon ben Elazar says: [The word sha'atnez suggests that] he [the transgressor] is naloz and causes his Father in heaven to meliz from him" (Mishna Kil'ayim 9:8). Rabbeinu Ovadya interprets the root "loz" based on the verse: "My son, let them not depart [yaluzu] from your eyes" (Mishlei 3:21).
According to this, R. Shimon ben Elazar says: He separates himself and causes his Father in heaven to separate from him, that is to say, his Father in heaven that is found in his heart. A person who fulfills his destiny in the world is a footstool of the Shekhina (adam [man] = hadom [footstool]), as Chazal said: "The patriarchs themselves are the chariot, as it is stated: 'And God ascended from upon Avraham' (Bereishit 17:22); 'And God ascended from upon him in the place where He spoke with him' (Bereishit 35:13); "And behold, the Lord was standing upon him and said' (Bereishit 28:13) (Bereishit Rabba 47:8)." Therefore, he is called man, when he keeps his sanctity, when he rules his passions and lusts and dedicates all his powers to God's service as a free man, and his entire goal is to fulfill His holy will….
THE ALLOWANCE OF SHA’ATNEZ IN TZITZIT AND IN THE PRIESTLY GARMENTS
We were only commanded to restrain and restrict the demands of our desires when our spirits and corporeal lives are not yet totally dedicated to the will of God. But when we are dedicated to the Holy One, blessed be He, in every fiber of our bodies, even in our basest impulses, as such impulses are found even in plants, when we dedicate even our carnal lives to the elevation of the name of God, and not to our own pleasure and delight, we are similar to the High Priest. Accordingly, we, together with our bodily and even vegetative impulses, are close to God, holy and pure; there is no contradiction or aspiration to go down from that moral virtue. We are free in our spirits and in our Divine morality, and all directions of life stand at the same level before God. It is therefore possible to understand that there is no prohibition of sha'atnez at that level, as Chazal say: "Everyone agrees that the girdle of the high priest on Yom Kippur was made of fine linen, and during the rest of the year of kil'ayim" (Yoma 12b).
Following this examination of sha'atnez, we return to the examination of the value of wool and linen as materials that were used in the Temple. Based on our examination, we can say: The concept "Mikdash" teaches us what we must give and to what we must dedicate ourselves in order to fulfill His great and holy will, by way of which we ourselves will become sanctified. The concept "Mishkan" shows us the blessings that God will bestow upon us, after we have fulfilled His holy will. Therefore, wool and linen can serve as symbols of all that clothing symbolizes. (ibid.)