פרשת אחרי מות תשי"ד - איסורי עריות

I am God God loves someone who withdraws from the world in order to serve Him and to understand His words (for example, men and women had to separate from one another three days before the revelation at Sinai). This mystery applied to the very first man [comment on Genesis 1:6] and is intrinsic to the human condition. Since human impulses are animalistic by nature, it was not feasible to forbid all women; but He did forbid all those with whom one is constantly in contact (In the parasha of Ki Teṣeh I shall further reveal a deep and hidden mystery [comment on Deuteronomy 23:10]). The phrase I am God suggests that by dirtying oneself carnally, one distances himself from the Holy and Revealed Name.

איש איש אל כל שאר בשרו לא תקרבו; logic would suppose that offspring from genetically related parents would result in superior human beings, evenly matched ones, as for instance in the case of Amram and Yocheved, where the marital union of aunt and nephew produced three outstanding human beings such as Miriam, Aaron, and Moses. In fact, the Talmud Yevamot 62,63 praises someone who marries his niece by quoting Isaiah 58,9 who calls down a special blessing from heaven on such a person. [“Then when you call, the Lord will answer, when you cry, He will say: ‘Here I am.’”]
The considerations I have just mentioned are valid only if both parties to such a marital union are motivated exclusively by the desire to carry out G’d’s will as they perceive it. However, truth to tell, this occurs in only rare cases. The vast majority of people, when choosing their mate, are driven by the desire to gratify their libido. Compare Psalms 51,7 הן בעוון חוללתי ובחטא יחמתני אמי, “Indeed, I was born with iniquity; with sin my mother conceived me.”
Seeing that genetically close relatives, usually living under the same roof, provide ample opportunity for the males and females of that family to engage in illegitimate sexual relations, and not only do they find it enjoyable but they do not consider it at all sinful, such pairings will hardly ever be for the purpose of marriage, but merely for the purpose of mutual physical indulgence. As a result, allowing marital relations of an incestuous nature would result in sexual promiscuity of major dimensions. This is why the Torah wrote לגלות ערוה, in most instances the very baring of flesh, and especially private parts, is the physical gratification desired in the first instance. This is why the Torah, in order to nip incest in the bud, addresses itself again and again to this phenomenon by using the expression לגלות ערוה, the titillation provided by feasting one’s eyes on the flesh of the opposite sex. When listing degrees of blood relationship, the Torah proceeds from the man’s vantage point, and in the case of the woman from the perspective of her husband. This is why in order of sequence the Torah first forbids the sister of one’s father who is a first degree blood relation to one’s father. On the other hand, the Torah permits the daughter of such father who is a relative of the second degree to the party. The Torah then prohibits the wife of one’s father and the wife of one’s brother and the wife of one’s uncle, even after their respective husbands have already died. This is in spite of the fact that no genetic connection exists between the people forbidden to one another as man and wife. The reason is simply that they Torah views them all from the perspective of how they are related to their husbands. This appears to be the guideline for all incest-related legislation.

ואת חקתי תשמרו AND KEEP MINE ORDINANCES — matters which are decrees of the King (promulgated without any reason being stated) against which the evil inclination raises objections: "Why should we observe them and against which also the nations of the world raise objections, as e. g., the prohibition of eating swine’s flesh, of wearing clothes of a mixture of wool and linen, the purgatory power of "water mingled with the ashes of the Red Heifer" (טהרת מי חטאת) — therefore it is stated: "I", the Lord, have enacted this for you — you are not at liberty to evade the obligation (Yoma 67b).

You shall keep my statutes: [And he cites the words of Rashi above]. But our Rabbis only mentioned that the reason is hidden and that the evil inclination and the idolaters question them about the wearing of shatnez (clothes made from linen and wool together), and not about forbidden mixtures of animals. And the intention about them is not that there be any decree of the King of the kings of kings in any place without a reason, since 'every word of God is pure' (see Proverbs 30:5). Rather, statutes are decrees of a king who imprints it with his authority without revealing their purpose to the people; such that the people do not benefit from them but rather question them in their hearts. Yet they accept them out of fear of the monarchy. So too, the statutes of the Holy One, blessed be He, are secrets that He has in the Torah that the people do not benefit from, according to their thoughts. But all [of His laws] have a correct reason and a perfect purpose. And the reason for forbidden mixtures is that God created species in the world - in all of those with spirits, in plants and in animate beings - and gave them the ability to reproduce, such that the species survive with them forever, so long as He, may He be blessed, wants the world to exist. So He commanded that they be able to produce according to their species, and that they never ever change; as it is stated about all of them, "according to its species" (Genesis 1). And this is the reason that we breed animals one with the other; for the continuation of the species - just as men have conjugal relations with women in order to be fruitful and multiply. And one who crosses two species together, changes and denies [God's] act of creation, as if he is thinking that the Holy One, blessed be He, did not perfect His world completely, and he wants to help with His creation of the world [by] adding creatures to it. [Moreover,] species of animals will not give birth when one specie is crossed with another. And even those that are close enough in nature so as to give birth - such as mules [that are born from crossing horses and mules]; their seed will be excised, as [the resultant mixed-breeds] will not give birth. And behold, on account of these two things, the act of mixing species has already been rejected and abandoned. And the fruits of plants that have been mixed from two species also do not grow afterwards; such that both of the reasons mentioned exist in their prohibition. And this is the reason for "you shall not seed forbidden mixtures" - which is grafting, according to the opinion of our Rabbis. And it also prohibited planting forbidden mixtures; because when they derive sustenance one from the other, it changes their nature, as well as their form. And it is as if each seed is grafted from two species. And the prohibition of plowing with an ox and a donkey is because it is the way of all those that work the land to bring the pair from the same barn, such that they would come to mixing [them].

אני ה' אלהיכם I AM THE LORD YOUR GOD — I am He Who spoke on Mount Sinai “I am the Lord thy God" and Whose kingship you then accepted; now, therefore, accept My decrees! Rabbi Judah han-Nasi said: It was manifest and known to Him that in the days of Ezra they would ultimately revolt against restricting sexual relations, He therefore came to them with a decree emphasized by the words: "I am The Lord your God" — understand well Who it is that imposes this decree upon you, — the Judge (אלהיכם) Whose function it is to punish but Who is certain also to give a reward ('‎ה‎) (cf. Sifra, Acharei Mot, Section 8 1).

כמעשה ארץ מצרים AFTER THE DEEDS OF THE LAND OF EGYPT… [SHALL YE NOT DO] — This tells us that the deeds of the Egyptians and the Canaanites were more corrupt than those of all other nations, and that the district of Egypt in which the Israelites had resided (אשר ישבתם בה) was even more corrupt than all the rest of Egypt (Sifra, Acharei Mot, Section 8 3).

אשר אני מביא אתכם שמה [AND AFTER THE DEEDS OF THE LAND OF CANAAN] WHITHER I BRING YOU [SHALL YE NOT DO] — This again tells us that those Canaanitish clans whom Israel subdued were more corrupt than all the others of them (Sifra, Acharei Mot, Section 8 4).

ובחקתיהם לא תלכו NEITHER SHALL YE WALK IN THEIR ORDINANCES — What has Scripture left unsaid when it spoke of the deeds of the Egyptians and Canaanites that it felt compelled to add ובחקתיהם לא תלכו But by these latter words it refers to their social customs — things which have assumed for them the character of a law as, for instance, the frequenting of theaters and race-courses. Rabbi Meir, however, said: These (חקתיהם) refer to the "ways of the Amorites" (superstitious practices) which our Rabbis have enumerated (Shabbat 67a; Sifra, Acharei Mot, Section 8 8; cf. also Tosefta Shabbat 7).