Wearing Tefillin on the go: Should we wear Tefillin during the day? A talk by Jack Hodari @ The Habura

GEMARA: Since doves’ wings were mentioned in the mishna, the Gemara cites a related story: Rabbi Yannai said: Donning phylacteries requires a clean body, like that of Elisha, Man of Wings. The Gemara asks: What is the meaning of the statement that donning phylacteries requires a clean body? Abaye said: It means that one may not break wind while donning them. Rava said: It means that one may not sleep in them.

(13) All those who are exempt from the obligation to recite the Shema are exempt from the obligation to wear tefillin. If a minor knows [the importance of] guarding his tefillin, his father should obtain tefillin for him, to educate him regarding the performance of mitzvot.
A person with stomach problems and anyone who can contain his excretory functions only with difficulty are exempt from the obligation to wear tefillin. [In contrast,] all those ritually impure are obligated to wear tefillin like one who is pure.
A person who suffers discomfort, or someone who is disturbed and cannot concentrate his thoughts, is exempt from the obligation to wear tefillin, since a person who wears tefillin is forbidden to divert his attention from them.
Priests who are in the midst of [the Temple] service, Levites who chant on the platform, and Israelites while they are attending the Temple [ceremonies] are exempt from the obligation to pray and to wear tefillin.

(14) A person should touch his tefillin [from time to time] during the entire time he is wearing them, so that he will not divert his attention from them even for a single moment, for their holiness surpasses that of the tzitz. The tzitz has God's name [written] upon it only once, while the head tefillin - and similarly, the arm tefillin - contain the Tetragrammaton 21 times.

(15) tefillin require a clean body; i.e., that one should be careful not to release gas while wearing them.
Accordingly, it is forbidden to sleep while wearing them - neither a long sleep nor a nap. If, however, one places a cloth over them and a woman is not with him, one may nap while wearing them. What should he do? Place his head between his knees and sleep while sitting.

(16) A person who has tefillin wound around his hand is permitted to sleep with them. [This applies] even to a long sleep.
He may eat only a snack while wearing them. If, however, he enters to partake of a regular meal, he should remove them and place them on the table until after he washes his hands [at the conclusion of the meal]. Afterwards, he should put them on and recite grace over his meal while wearing them.

(25) The holiness associated with tefillin is very great. As long as a person is wearing tefillin on his head and arm, he will be humble and God-fearing and will not be drawn to frivolous behavior or empty speech. He will not turn his thoughts to evil matters, but rather will direct his heart to words of truth and justice.
Accordingly, a person should try to wear [tefillin] throughout the entire day, for this is the mitzvah associated with them. Among the praises conveyed upon Rav, the student of Rabbenu Hakadosh, was that he was never seen walking four cubits without [reciting words of] Torah, without tzitzit, and without tefillin.

(26) Although it is a mitzvah to wear [tefillin] throughout the entire day, it is most important during prayer. Our Sages declared: "Whoever recites the Shema without tefillin is considered as if he is giving false testimony."
Whoever does not wear tefillin transgresses eight positive commandments, for in each of the four passages contained in the tefillin we are commanded to wear both head and arm tefillin. [The rewards for wearing tefillin are also great.] Whoever wears tefillin regularly will live long, as [implied by Isaiah 38:16]: "God is upon them, they shall live."

(1) One who is ill in his intestines is dispensed from the [commandment to wear] tefillin. Rema: "Even if he is not in pain. However [regarding] all other sick people, if he is in pain due to his illness and his mind is not at ease, he is also dispensed [from the commandment]. Otherwise he is obligated."

(2) One to whom it is clear that he cannot pray without flatulating, it is better that the time for Tefilah (the Shemoneh Esreh) should pass rather than that he should pray without a clean body. (And see further section 80.) And if it appears to him that he will be able to control himself to have a clean body [i.e. not flatulate] at the time of reading the Shema, he should put on tefillin between [the blessing just prior to Shema, ending in] Beahava and Shema, and bless [upon the tefillin].

(3) Women and slaves are exempt from Tefillin because it is a positive commandment which is caused by time. Rem"a: And if the women want to be stringent for themselves, we protest against it (Kol Bo).

(4) One who wears tefillin must be cautious to avoid thoughts about desire for a woman. Rema: "And if it's impossible for him not to think [about this desire] it is better not to put on tefillin."

(8) Scribes writing tefillin and mezuzot, them, their distributors and their distributors' distributors, and all those involved in the work of Heaven, are dispensed from wearing tefillin all day long, except [that they must wear them] at the time of reading Shema and [of] the Tefilah (Shemoneh Esreh). Rema: "And if they had to do their work at the time of reading Shema and of the Tefilah, they are dispensed of Shema and Tefilah and tefillin, for everyone who is involved in a mitzvah is dispensed from engaging in another mitzvah if one has to make an effort for the other mitzvah. However if he can do both mitzvot without exerting himself, he should do both. (Quoted from Hagahot Ashrey in the name of Or Zarua and RaN on the Talmudic Chapter "The Sleeper.")

(9) On who is distressed, and one who's mind is not settled and ready is exempt [from תפילין] since it is forbidden to take one's mind off of them.

(10) One who reads from the Torah (ie. he is in the middle of learning Torah) is exempt from wearing תפילין the entire day, except for when he is saying Shema and Tefillah (ie. Shmonah Esrei).

Summary:

Rosh believes that one can nap with Tefillin on (see Berakhot 23b). How does that reconcile with the requirement of not forgetting that you are wearing the Tefillin (hesekh hada'at)?

R. Yona said (based on Rambam) that hesekh hada'at is only when one is joking around (kalut rosh and sehoq). But if you stand with awe and do what you need to do, even if that is work, and you are not literally thinking about the Tefillin, that is not called hesekh hada'at (which would therefore indicate no issue with wearing Tefillin whilst working).

Otherwise, how could anyone wear Tefillin all day (as discussed in the Gemara)? Similarly, when someone sleeps that is not called hesekh hada'at because they are taking their mind off useless things and there is no kalut rosh.

And [also] that which they said (Shabbat 49a) that tefillin requires a clean body, and they said in the Gemara, "What is a clean body? That he be careful not to pass gas with them [on]." But the matter is not to say that it requires a body clean of sins or of impurity. As every man, even one impure or a sinner is obligated about the commandment of tefillin, so long as he knows to be careful not to pass gas with them [on]. And maybe from being constant with the commandment of tefillin - as they are a great memory device for a person about his service to the Heavens - he will repent from his evil way and purify himself from all of his filth.

And the Sages, may their memory be blessed, obligated us about the commandment of tefillin to educate even the small youths about it, so long as they have arrived to the category [of those] that know to guard them. And from here it can be understood that the opinion of our Rabbis, may their memory be blessed, was that every man should grab onto this commandment and be accustomed to it, since it is a great fundamental, a protection from sin and a strong ladder to climb with to enter into the service of the Creator, blessed be He.

And maybe the intention of those that are stringent about the holiness of the commandment, and discourage the hearts of the masses with their words from being involved with it, is good. But in truth, through this, there is the prevention of people from several commandments, and [so] it is a great evil.

And [this is] even though I know that those that preach these lessons base themselves on the Talmud Yerushalmi Berakhot 2:3, "About a certain man who deposited a glass with his fellow, and afterwards demanded it [back] from him and [the other] denied [having it]." And the owner of the glass said to him, "'It is not you that I trusted, but that which is on your head that I trusted'" - and their intention is to say that there is a desecration of God's name, to be pious about some commandments and to be evil about others. But this is not my home with God (not how I understand the ways of God); as I know that 'there is no righteous man in the world who does good and never sins,' and nonetheless he is not prevented from being involved with commandments when the good spirit of God clothes him to do the good. As who knows whether maybe he will continue in his good path until the time of his death - and death will come suddenly.

And they, may their memory be blessed, have already taught us (Avot 4:2) that "a commandment leads to another commandment" and "the reward for a commandment is another commandment." About all of these things and the good ethics, they, may their memory be blessed, have preceded us and taught us. And those that want to be wise and add upon their words or take away [from them] are not [involved in] wisdom.

It is from the root of the commandment [that] since people are physical, they are necessarily drawn after their desires [...]

And the Omnipresent, blessed be He, wanted to give us - the holy nation - merit, and [so] He commanded us to set up mighty guards around [the soul].

And they are that we were commanded not to interrupt from [speaking] words of Torah from our mouths day and night; that we place four fringes on the four corners of our garments; a mezuzah on our doorpost; and the tefillin on our arm and on our head. And all of this is to remind us to avoid the crimes of our hands and that we not stray after our eyes or after the impulse of the thoughts of our hearts. Therefore, they, may their memory be blessed, said (Zevachim 19a) that the priests and the Levites are exempt from them when they performed the [Temple] service. And as the foundation of the tefillin is as we have mentioned, we are commanded about them (Menachot 36b) that we not remove our thoughts from them.

Now, my son, also see how much more power our bodies have than our souls; for despite all this, it sometimes comes up and 'breaks our fence.' May God in His mercy aid us and protect us, amen.

And it is practiced in every place and at all times by males, but not by females; because it is a positive commandment determined by time. And nonetheless, if they want to lay tefillin, we do not protest [against them] and there is reward for them; but not like the reward of a man - as the reward of someone who is commanded [something] and does [it] is not similar to the reward of someone who is not commanded [it] and does [it] (Kiddushin 31a). And in Tractate Eruvin 31a in the chapter [entitled] Hamotseh Tefillin, they, may their memory be blessed, said that Michal the daughter of Shaul would lay tefillin and the Sages did not protest [against her]. And there they [also] said the wife of Yonah would go up in pilgrimage and the Sages did not protest [against her].