Halakhah su Levitico 25:37

He prohibited being involved with a loan with interest between a borrow and a lender - not to be a guarantor for one of them, not to be a witness for them and not to write a contract about what they agreed upon about the interest. And that is His saying, "you shall not lay upon him interest" (Exodus 22:24). And the language of the Gemara, Metzia (Bava Metzia 75b), is "The guarantor and the witnesses only transgress on account of, 'you shall not lay.'" And there, it is explained that the scribe, the witnesses and the guarantor also transgress. And there, it is also explained that this negative statement, which is 'you shall not lay' - even with its coming about the middlemen, meaning those [tangentially] involved in that matter - also includes the lender. And therefore the lender transgresses six negative statements: The first is, "do not be to him as a creditor" (Exodus 22:24); the second is, "Your money you shall not give him on interest" (Leviticus 25:37); the third is, "and on increase you shall not give your food" (Leviticus 25:37); the fourth is, "Do not take from him" (Leviticus 25:36); the fifth is, "you shall not lay upon him"; and the sixth is, "and you shall not put a stumbling block in front of the blind" (Leviticus 19:14). And there, they said, "These transgress a negative commandment: The lender; the borrower; the guarantor; and the witnesses. And the Sages say, 'Even the scribe.' They transgress, 'you shall not give him'; 'Do not take'; 'do not be to him as a creditor'; 'you shall not lay'; and 'you shall not put in front of the blind.'" And in the Gemara: "Abbaye says, 'The lender transgresses them all; the borrower transgresses, "You shall not charge interest" (Deuteronomy 23:3) and "and you shall not put a stumbling block in front of the blind"; the guarantor and the witnesses only [transgress] on account of "you shall not lay."'" And one who transgresses this negative commandment: If the interest was fixed, we take it away from him and return it to the one from whom it was taken. (See Parashat Mishpatim; Mishneh Torah, Creditor and Debtor 4.)

To not lend with interest to an Israelite: To not lend with interest to an Israelite, as it is written (Leviticus 25:37), "You shall not give your money with interest, nor should you give your sustenance with increase." And these are not two prohibitions - as increase is interest, and interest is increase; and as they, may their memory be blessed, said in [Bava] Metzia, "You will not find interest without increase or increase without interest. So why did the verse divide them?" [That is] meaning to say, why did it divide them and not write, "Give neither your money nor your food with interest." "To cause the transgression of two prohibitions" - meaning to say, to give multiple warnings about it (Bava Metzia 61a). And this matter is what I have said above (Sefer HaChinukh 336), that the Torah will occasionally repeat warnings about that which it wanted to distance us from greatly. And it is possible for us to say about this, similar to what they, may their memory be blessed, said about other matters, "The Torah speaks like the language of man" (Berakhot 31b). And likewise, the Torah is constantly warning about that which requires our vigilance in the way that people will repeat their conditions and speak much when they warn one another about a weighty matter - so that the [listener] be aware and vigilant about it in all circumstances. And even though it is fitting that a person should be most careful about the word of God - even if he heard the word through the slightest hint - this is all from His great kindnesses upon His creatures, that in a few places He repeated warnings for them many times - like a parent disciplines his child. And we should therefore thank Him for all the goodness that He, blessed be He, bestowed upon us.