You may not cause your brother to accept interest… (Deuteronomy 23:20)
In Mitzvah #68, we had the prohibition against participating in an interest-bearing loan as a witness or a co-signer. In Mitzvah #343, we had the prohibition against lending to another Jew with interest. Here, we have the prohibition against borrowing from another Jew with interest.
One might think it’s permissible to borrow with interest–if the borrower wants to be taken advantage of, why not let him pay extra? Here we see that such is not the case. Interest-bearing transactions are inherently objectionable to God and one may not participate in any capacity, not even as the borrower.
The reason for this is what we have said before about interest: a loan is supposed to be an act of kindness. Charging interest turns it into the exact opposite, as the lender takes advantage of the borrower’s needs. As we said, God doesn’t want this to happen even if the borrower is willing.
Rabbinically, as long as a debt is outstanding, a borrower may not do favors for the lender that he would not have done otherwise. He may not flatter or even go out of his way to greet the lender because of the loan. This is called “ribbis devarim” – interest with words. It may have no financial value but it is clearly a benefit the lender reaps on top of repayment. (After the loan has been repaid, the borrower may do as many nice things for the lender as he wishes.)
This mitzvah applies in all times and places. It is discussed in the Talmud in tractate Baba Metzia on pages 75a-b. It is codified in the Shulchan Aruch in Yoreh Deah 160. This mitzvah is #236 of the 365 negative mitzvos in the Rambam’s Sefer HaMitzvos and #55 of the 194 negative mitzvos that can be observed today as listed in the Sefer HaMitzvos HaKatzar of the Chofetz Chaim.