Charging interest
Whether the prohibition of interest binds all lending or only loans within the community, and whether the two laws differ.
Exodus 22:25-27
25“If you lend money to any of my people with you who is poor, you shall not be to him as a creditor. You shall not charge him interest.
26If you take your neighbor’s garment as collateral, you shall restore it to him before the sun goes down,
27for that is his only covering, it is his garment for his skin. What would he sleep in? It will happen, when he cries to me, that I will hear, for I am gracious.
Deuteronomy 23:19-20
19You shall not lend on interest to your brother: interest of money, interest of food, interest of anything that is lent on interest.
20You may charge a foreigner interest; but you shall not your brother interest, that Yahweh your God may bless you in all that you put your hand to, in the land where you go in to possess it.
What each tradition says
Rabbinic / Midrashic
The Jewish Encyclopedia says three Biblical passages forbid taking interest in the case of “brothers” but permit, or seemingly enjoin, it when the borrower is a Gentile. It cites Exodus 22:24, Leviticus 25:36-37, and Deuteronomy 23:20-21.
Executive Committee of the Editorial Board; Lewis N. Dembitz; Joseph Jacobs, The Jewish Encyclopedia (1905), art. "Usury" (redirected from "Interest") — Section 'Case of a Gentile'
Patristic
Augustine says that if you lend money to someone and expect to receive back more than you gave—whether in money, wheat, wine, oil, or anything else—you are a usurer. In this matter, he says, you are not deserving of praise but of censure.
Augustine, Expositions on the Psalms (Nicene and Post-Nicene Fathers, First Series, Vol. 8; J.E. Tweed trans.) — Psalm 37, §5
Catholic
Vermeersch says no absolute prohibition of interest can be found in the Old Testament. At most, Exodus 22:25 and Deuteronomy 23:19-20 forbid one Jew from taking interest from another.
Arthur Vermeersch, The Catholic Encyclopedia (1912), art. "Usury" — Opening section
Orthodox
Philaret’s Longer Catechism treats usury as extortion: creditors oppress debtors by usury, making their own advantage of others’ property against equity and humanity under the show of right. The same extortion includes excessive imposts or tasks and selling bread at exorbitant prices in famine.
Philaret of Moscow, The Longer Catechism of the Orthodox, Catholic, Eastern Church (R.W. Blackmore trans.; in Schaff, Creeds of Christendom) — Part III, Q. 593 (On the Eighth Commandment)
Reformed / Protestant
Calvin holds that under the political law God permitted His people to receive interest from Gentiles, since otherwise a just reciprocity would not be preserved. The command not to practice usury bound the Jews alone, not foreign nations.
John Calvin, John Calvin's Bible Commentary (Calvin Translation Society) — On Exodus 22:25
Evangelical
Wesley says the law forbade receiving interest from anyone who borrowed out of necessity. Since the people had little concern in trade and the Jubilee preserved estates to their families, borrowing among themselves was generally for necessity, so it was generally forbidden among them. To a stranger they were allowed to lend upon interest.
John Wesley, Explanatory Notes upon the Old Testament — Note on Exodus 22:25