Q. Since the Bible forbids taking interest, how does this apply to commercial lending?
A. The rule in the Torah is more concerned with individuals borrowing from one another. The Talmudic sages said that “all payment for waiting for one’s money is prohibited” (Bava Metzi’a 63b). In this sense “payment” includes social deference, e.g. greeting your lender especially politely when you see him in the street.
Commercial transactions, which are much more complex, were already known in Talmudic times and to avoid problems various devices were worked out which, for example, gave the borrower and lender the status of business partners with the active partner paid for his efforts. This does not contravene the Torah but promotes the spirit of “that your brother may live with you” (Lev. 25:36).