Midrash su Deuteronomio 31:19

(Exodus 21:1) "And these are the judgments": R. Yishmael says: "And these" — What follows is being added to what precedes, viz.: Just as what precedes was stated at Sinai, so, what follows. R. Akiva says: What is the intent of "And these are the judgments"? From (Leviticus 1:2) "Speak to the children of Israel and say to them," I would think, only once. Whence do I derive that it is to be repeated two, three, and four times until it is assimilated? From (Devarim 31:19) "and teach it to the children of Israel." I might think that it is to be taught but not repeated. It is, therefore, written (Ibid.) "Place it in their mouths." I might think that it is to be repeated (even) if it is not understood. It is, therefore, written "And these are the judgments." Set them out before them as a set table, as it is written (Ibid. 4:35) "You have been shown to know, etc."

GEMARA: Rabba said: "Even if his ancestors left one a scroll, nevertlieless it is a meritorious act for him to write the Holy Scrolls at his own expense, as it is said (Deut. 31, 19) Now, therefore, write this song." Abaye objected [from our Mishnah]: "He shall write the Holy Scrolls for himself," and must not be satisfied with those of his parents. And this speaks only of a king, but not of an ordinary man. Our Mishnah treats of two Holy Scrolls, as we are taught in the following Baraitha (Ib. 17, 18) He shall write for himself a copy of this law — i.e., He must write for himself two Holy Scrolls, one which he must carry wherever he goes, and one which shall remain in his treasury. The one he has to bear with him he shall write in the form of an amulet, and place it on his arm, as it is said (Ps. 16, 8) I have always set the Lord before me. However, he must not enter a bath or a toilet with it, as it is said (Ib., ib. 19) And it shall be with him and he shall read; i.e., it shall be with him in those places where it is permitted to be read, but not in those places where it is not permitted.

Our Rabbis taught: "What was the method of learning the traditional Torah in the days of Moses? Moses learned it from the mouth of God, then Aaron entered and Moses taught him the chapter; when Aaron had finished, he left the seat of study, taking a seat at the left of Moses, and then his sons entered. Moses then taught them the chapter. When they finished, they departed, Elazar assuming a seat at the left of Moses and Ithamar at Aaron's right. R. Juda says: 'Aaron was always at the right of Moses.' The elder then entered and Moses taught them the same chapter. When the elders were through, they departed and the people entered and Moses taught them the chapter. Thus it is found that Aaron studies the chapter four times, his sons, three times, the elders twice, and the people once. Moses then departed and Aaron studied the same chapter with them all. When Aaron finished, he departed, and his sons studied the chapter with them; after the sons finished, they departed and the elders studied the chapter with the people. It is thus found that every one repeated the chapter four times. 'From this.' says R. Eliezer, 'we learn that it is the duty of a man to repeat a lesson with his disciple four times.' For if Aaron who learned it from Moses and if Moses, who learned it from God Himself, had to repeat the chapter four times, then, surely, an ordinary man who learns from another ordinary man, should repeat it much more frequently." R. Akiba said: "Whence do we infer that a man must learn the lesson with his disciple until his disciple knows it? It is said (Deu. 31, 19.) And teach it the children of Israel. Whence do we know that he must teach him until he knows it? It is said (Ib. ib. ib.) Put it in their mouths. Whence do we infer that the he must show him the reasons for every law? It is said (Ex. 21, 1.) And these are the laws which thou shouldst place before them." Why should not all enter and learn directly from Moses? In order to show honor to Aaron, his children and the elders. If that be so, then why should not Aaron enter and learn it from Moses, Aaron's children from Aaron, the elders from Aaron's children, and the people from the elders? Because Moses learned from the Almighty, he was therefore more capable of explaining the Torah. The master said above: R. Juda says "Aaron was always sitting to the right of Moses." In accordance with whose opinion is the following Baraitha? "When three men are walking on the road the teacher shall walk in the middle, the junior disciple to his right and the senior to his left." Is this not in accordance with B. Juda [who says Aaron was sitting at the right of Moses]? We can say it is in accordance even with the opinion of the Rabbis, yet Aaron occupied his seat to the right of Moses in order to save him trouble [as he occupied the seat at the right of Moses in the beginning, so he remained].