Midrash su Deuteronomio 23:20

Another matter, “who is like the wise man” – this is the Torah scholar. “And who knows the meaning of a matter” – as he knows how to interpret his learning.⁹He knows how to arrive at halakhic conclusions. “The wisdom of a man [illuminates his face]” – when he is asked a question and responds; “and the boldness of his face is changed” – when he is asked a question and does not know how to respond.
Rabbi Ḥiyya was sitting and teaching: From where is it derived that one cannot substitute for a firstborn?¹⁰A firstborn kosher animal has sanctity and must be given to a priest (see Deuteronomy 15:19–23). If one attempts to transfer the sanctity to a different animal, both animals are considered sacred. However, once the firstborn animal is given to the priest, if one attempts to transfer the sanctity to a different animal, the attempt is meaningless, and the second animal is not considered sacred. This is the teaching that Rabbi Ḥiyya was explicating. The face of bar Pedaya glowed. [Rabbi Ḥiyya] said: This one knows what I am sitting and teaching.
A certain gentile saw Rabbi Yehuda ben Rabbi Ilai; he saw that his face glowed. He said: ‘This man is one of three things; either he is intoxicated with wine, lends with interest, or raises pigs.’ Rabbi Yehuda ben Rabbi Ilai said: ‘Let despair come upon that man, as I do not have even one of the three. I am not a lender with interest, as it is stated: “Do not lend to your brother with interest” (Deuteronomy 23:20). I am not a raiser of pigs, as it is prohibited for an Israelite to raise pigs, as it is taught there: It is prohibited for a person to raise pigs anywhere.¹¹Mishna Bava Kama 7:7. And I am not intoxicated with wine, as even the four cups of wine that I drink on Passover eve cause my head to ache from Passover until Shavuot.’¹²Rabbi Yehuda bar Rabbi Ilai did not like wine and would not drink it unless absolutely necessary. [The gentile] said to him: ‘Why does your face glow?’ He said to him: ‘It is my Torah that causes my face to glow, as it is written: “The wisdom of a man illuminates his face…”’
Rabbi Abbahu went to Caesarea and he came from there and his face was glowing. His students saw him and ascended and told Rabbi Yoḥanan: ‘This Rabbi Abbahu found a treasure.’ He said to them: ‘Why [do you say so]?’ They said to him: ‘Because his face is glowing.’ He said to them: ‘Perhaps he heard some new Torah.’ They ascended to him and they said to him: ‘What new Torah did the Master hear?’ He said to them: ‘An ancient Tosefta was cited.’ They recited a verse in his regard: “The wisdom of a man…”

3) "and your brother shall live with you": This was expounded by Ben Patori: If two men were walking along the road and one of them had only a kiton of water — If one of them drinks it, he will reach the settlement; if both of them drink it, they will both die — Ben Patori expounded: Let them both drink it and die, it being written "and your brother shall live with you" (i.e., "as you do"). R. Akiva said to him "and your brother shall live with you" — your life comes before that of your neighbor. (Vayikra 25:37) ("Your money you shall not give him on interest, and on increase you shall not give your food.") "your money": and not the money of others (i.e., gentiles); "and your food": and not that of others. — But perhaps (the meaning is) "your money," but not the money of ma'aser; "your food," but not animal food! (This cannot be maintained, for it is written [Devarim 23:20]) "interest of money" — to include the money of ma'aser; "interest of food" — to include animal food. "and on increase you shall not give your food. (Devarim 23:38) I am the L–rd" — whence they stated: One who takes upon himself the yoke of (shunning) interest takes upon himself the yoke of Heaven, and one who divests himself of the yoke of (shunning) interest divests himself of the yoke of Heaven. (Vayikra 25:38) ("I am the L–rd your G d, who took you out of the land of Egypt to give to you the land of Canaan, to be a G d to you.") "I am the L–rd your G d, who took you out": It is on this condition that I took you out of the land of Egypt — that you take upon yourselves the mitzvah of (shunning) interest. For all who acknowledge the mitzvah of (shunning) interest acknowledge the exodus from Egypt, and all who deny the mitzvah of (shunning) interest, it is as if they would deny the exodus from Egypt.

Our rabbis teach us that the borrower, the guarantor, the witnesses, and the scribes are all considered culpable, (for without them the moneylender would not have loaned his money on interest). Therefore, all of them shall be punished. Whence do we learn that the borrower is punished? It is written: Thou shalt not cause thy brother to lend upon interest (Deut. 23:20). To what can interest be likened? To a person who does not feel or notice the bite of a snake until the swelling appears. Similarly, interest is not felt until it has increased for the debtor. If thou at all take thy neighbor’s garment to pledge (Exod. 22:25). The Holy One, blessed be He, said to him: If he is in debt to you, you are also in debt to Me, as it is said: If they sin against Thee—for there is no man that sinneth not (I Kings 8:46).