Siman 37

Great is the mitzvah of tefillin, for anyone who dons them lengthens his days, as it is said: "O Lord, upon them they shall live" (Menachot 44a) – those who carry upon them the name of the Lord, which are tefillin, shall live (Rashi). And it is brought in Shimusha Rabba that anyone who dons tefillin, and wraps himself in tzitzit, and recites Kiryat Shema, and prays – is assured that he is a member of the World to Come. And the fire of Gehinnom does not rule over him, and his iniquities are forgiven (Tur). And in Berakhot (15a) we say: Anyone who relieves himself, and washes his hands, and dons tefillin, and recites Kiryat Shema, and prays – it is as if he built an altar and offered a sacrifice upon it; see there. And anyone who does not don tefillin transgresses eight positive commandments (Menachot ibid.). For in the four parashiyot of tefillin, the shel yad and the shel rosh are written, and each one is a positive commandment unto itself. And anyone who does not don tefillin is called a "transgressor of Israel with his body" (Rosh Hashanah 16a). Therefore, every man of Israel must be careful with this great mitzvah. And he should seek out a God-fearing sofer, and beautiful and adorned tefillin. And he should remember that he does not buy tefillin every day nor every year, and it is for many years. And how can he stint on a small amount of money for a great mitzvah that lasts for many years?

And there is one who divides this sin into three categories. That is, one who does not don them because they are contemptible in his eyes is a "transgressor of Israel with their body," and regarding them they said in Rosh Hashanah (17a): they are judged for generations upon generations in Gehenna. And one who does not don them because he does not want to be idle from his work is also a "transgressor of Israel with his body," and is judged in Gehenna for twelve months. But one who does not don them because he is concerned that his body is not clean—he is not included in "transgressor of Israel." However, there is a sin in his hand, for every person is able to be careful for the short time of the recitation of Shema and prayer. Thus wrote the Rosh, of blessed memory (Bach).

The Tur and Shulchan Aruch wrote: Their mitzvah is to be upon him all day. However, because they require a clean body, that he should not flatulate in them and that he should not divert his attention from them, and not every person is able to be careful with them—it has become the custom not to don them all day. And every person must be careful with them, to have them upon him during the time of the recitation of Shema and prayer. Thus far their words, meaning: certainly the obligation of the mitzvah from the Torah is fulfilled by donning them one hour in the day, during the time of the recitation of Shema and prayer. And only if he did not don them at all once during the day has he nullified a positive commandment. But there is no obligation to wear them all day. Rather, certainly since it is a great mitzvah among the greatest, which contains the unification of Hashem and His fear and His love, may He be blessed, and the yoke of commandments—it is proper to wear them all day. And so was the custom of our teachers, the sages of the Mishnah and the Gemara, and the Rabbanan Savorai and the Geonim. And regarding this our teachers say that now it is not the custom in this. And there are those from whose words it is implied that one who wishes now to don them all day, in his confidence that he will not flatulate and will not divert attention, nevertheless should not don them all day (see Magen Avraham, subsection 2). And in my humble opinion it does not appear so. And so we have heard that there are unique individuals, and especially in the generations before us, who would wear them all day. And now the remaining unique individuals have also practiced to study a little in them after the prayer. (See there in the Magen Avraham, who brought from a responsum of the Rema mi-Fano that he instituted to don them a second time at Mincha. And happy is their lot.)

A minor who knows how to guard tefillin in purity, that he should not flatulate in them and not sleep in them, and not enter a beit hakise with them—his father is obligated to buy him tefillin to train him. But prior to this, it is forbidden to give him tefillin. And there are those who say that this minor is specifically when he is thirteen years and one day old. And so they practiced and one should not change (Rema), and prior to this they do not don them. And now they have practiced to don them two or three months before the time (Magen Avraham subsection 4). And now they begin a month before. And there are those who do not begin at all beforehand. And many rejected the opinion of the "there are those who say," for if it is when he is thirteen years and one day old—it is obvious, for behold he is obligated in all the mitzvot. And also the obligation is cast upon him himself (Bach, and Eliyah Rabbah, and Pri Megadim, and the Gaon Rabbi Akiva Eiger). And there are those who explained: even though he did not bring two hairs (the Gaon Rabbi Akiva Eiger and so it is implied in the Pri Megadim, see there). And in truth it is a singular opinion, the opinion of the Ittur, and our teacher, the Beit Yosef, in his great book rejected this, as is implied from all the Rishonim that it is a literal minor, see there. And in my humble opinion it appears that certainly according to the core of the law it is so like the opinion of all the Rishonim. Rather, this was in the time of the Talmud when they were separate and diligent, but now one should not practice so. And for this they wrote that so they practiced and one should not change, meaning: that now it is impossible to rely on any minor when he is before thirteen years, and would that they be careful with the sanctity of tefillin when they are thirteen years old. And know that it is common in the mouths of the masses that an orphan should begin a year before to don tefillin. And I do not know any reason for this, and it is not correct to practice so for the reason we explained. And a deaf-mute and an imbecile—certainly one should not give them tefillin, for certainly they will not be careful with their sanctity.