Komentarz do Powtórzonego Prawa 31:19

That is that He commanded us that every man among us should write a Torah scroll for himself. And if he writes it with his hand, Scripture accounts it to him as if he received it at Mount Sinai. But if it is impossible for him to write it, he should buy it or hire someone to write it for him. And this is His saying, "write for yourselves this song " (Deuteronomy 31:19). And it is not permitted to write [only] sections. For when He said, "this song," He intended the whole Torah, which includes this song (of Haazinu). And the language of the Gemara (Sanhedrin 21b) is, "Rabbah said, 'Even if his ancestors left him a Torah scroll, it is a commandment to write a scroll of his own, as it is stated, "write for yourselves."' Abaye raised an objection to him (from a baraita concerning the king’s Torah scroll), '"And he writes himself a Torah scroll for himself, so that he does not become proud from the Torah scroll of his ancestors." A king, yes, but an ordinary person, no!'" And the answer was, "No, [the ruling of that baraita] was only necessary [to teach that the king is commanded to write] two Torahs; as it is taught in a baraita, 'And he must write two Torahs for himself.'" This means to say that the difference between a king and an ordinary person is that every man is obligated to write a Torah scroll, whereas a king, two - as it is explained in the second chapter of Sanhedrin. And the regulations of this commandment - meaning to say, the writing of a Torah scroll and its stipulations - have already been explained in the third chapter of Menachot and in Shabbat, Chapter 16. (See Parashat Nitzavim; Mishneh Torah, Tefillin, Mezuzah and the Torah Scroll.)

את השירה הזאת [NOW THEREFORE WRITE YE] THIS SONG — i.e. the text “Give ear, O ye heavens”, till “and make expiation for his ground, and his people” (Deuteronomy 32:1—43).

AND NOW WRITE YE THIS SONG. In line with the plain meaning of Scripture, He commands both Moses and Joshua to write it for He wanted to make Joshua His prophet during Moses’ lifetime. Now, Moses wrote it while Joshua stood by him, read it, and saw [it completed], this being the sense of the verse, So Moses wrote this Song the same day, and taught it the children of Israel.³⁶Further, Verse 22. It refers to Moses who was the principal [in the writing of the Song] for it was from him that they would hear it and learn it, although Joshua, too, taught it with him, as it is stated at the conclusion [of the chapter] he [i.e., Moses], and Hoshea, the son of Nun.³⁷Further, 32:44.
Now, the meaning of the expression this Song is “the Song that I will now tell you,” this being ‘Ha’azinu’ (Give ear).³⁸Ibid., Verses 1-43. It is called Song because Israel would recite it with song and psalm.³⁹At the Divine Service in the Sanctuary, a section of the Song of Ha’azinu was chanted each Sabbath during the Service of the Additional Offering. The cycle of the Song was completed every six weeks. Therefore, the six divisions (Aliyoth) in the reading of this Song in the Synagogue on the Sabbath of Ha’azinu, follow the same divisions as sung in the Sanctuary (Rosh Hashanah 31a). It was also written [in the Torah] in the style of a song, since songs are written with interruptions [empty spaces] indicating the places of chanting.