This Saturday, synagogues will chant the Torah portion of Mishpatim, from the book of Exodus, which is the source for the injunction against charging interest to a fellow Jew: "When you lend money to my people, to the poor among you, do not act toward them as a creditor; exact no interest from them."

Shana Novick, executive director of the Hebrew Free Loan Society of New York, explains that "Jewish tradition translated this biblical injunction into a powerful imperative: Help your neighbor in need...