Ramban: Because He wanted Moshe and Yehoshua to be involved in writing it, on order to establish Yehoshua as His prophet in the lifetime of Moshe. ¹ The Torah nevertheless writes " Velamdah es B'nei Yisrael" in the singular, because Moshe was the main teacher from whom they learned.

Sanhedrin, 21b: Because it is a Mitzvah for every person to write a Seifer Torah, ² even if he inherited one from his fathers.

Rashi, Ramban, Rashbam (in Pasuk 30), Targum Onkelos and Targum Yonasan: It is referring to the Parshah of "Ha'azinu" up to "Ve'chiper Admaso Amo" (32:43). ¹

Ha'Kesav ve'ha'Kabalah (citing the Ralbag) and Nedarim 38a: It refers to the entire Torah ² - and we learn from here the Mitzvah to write a Seifer Torah.

Ramban: Because He wanted Moshe and Yehoshua to be involved in writing it, on order to establish Yehoshua as His prophet in the lifetime of Moshe. ¹ The Torah nevertheless writes " Velamdah es B'nei Yisrael" in the singular, because Moshe was the main teacher from whom they learned.

Sanhedrin, 21b: It is a Mitzvah for every person to write a Seifer Torah, ² even if he inherited one from his fathers.

Eruvin, 54b #1: "Velamdah es B'nei Yisrael" implies that one should teach one's Talmid as many times as necessary for him to absorb the lesson, ¹ and "Simah be'Fihem" that he should teach him until he has organized it clearly in his mind. ²

Eruvin, 54b #2: "Simah be'Fihem" is a hint that one can only acquire the Torah via 'Simanim' ³ - 'Al Tikri "Simah", Ela 'Simnah'.

Ramban: Because it is always sung and played in the form of a Shirah, and because it is written in the form of a Shirah.

Rashbam (in Pasuk 30): Any arrangement of words is called a 'Shirah'.