Proverbs 28:8 makes it clear that usury is unjust gain: He that by usury and unjust gain increaseth his substance, he shall gather it for him that will pity the poor. Usury originated from the Latin term 'usus' which means a use. Usury is to make a profit from lending money to a debtor who is enslaved to the debt. The rich ruleth over the poor, and the borrower is servant to the lender (Proverbs 22:7).
Many Christians argue that it is only usury of the poor that is prohibited by the Bible. They use Exodus 22:25 which says "ff thou lend money to [any of] my people [that is] poor by thee, thou shalt not be to him as an usurer, neither shalt thou lay upon him usury" to justify their case for usury. However, usury itself is the extortion from another because it is unjust gain. Therefore, usury is a sin, on this ground alone. The affluence of the person who is forced to pay usury is absolutely irrelevant as to whether usury is wrong because usury itself is unjust gain.
Some Christian use Deuteronomy 23:19-20 to justify usury: Thou shalt not lend upon usury to thy brother; usury of money, usury of victuals, usury of any thing that is lent upon usury: Unto a stranger thou mayest lend upon usury; but unto thy brother thou shalt not lend upon usury: that the LORD thy God may bless thee in all that thou settest thine hand to in the land whither thou goest to possess it. They argue that usury against anyone was permitted except for that charged against a Jews, implying that God approves a usury, and therefore that usury is not a sin. However, regarding the Laws of God, it is what Jesus said to be sin that determine what is sin, rather than what Moses said.
In Matthew 19:8, Jesus said: "Moses because of the hardness of your hearts suffered you to put away your wives: but from the beginning it was not so." This is to say that it is not the Law of Moses that is binding on all of us, but the Law of God. In Matthew 21:12, Jesus was angered by the money lenders and called them 'thieves'. Jesus was angry at the money lenders because they used God's temple for business interests, and also because they were charging usury. Jesus, by calling them thieves, was in effect, saying that money lending, that is, usury, is stealing. Therefore, usury is a sin in God's eyes. Jesus' Words are the Ultimate Standard, not Moses.
Jesus cleared the Temple of the money-lenders to cleanse it because such an act is despicable, unholy, abominable and wicked. Money lending is not only to use of money to enslave people into debt, but to make a profit from economic slavery. Such an act is unjust and selfish, one that legitimises wealth generation from money itself rather than from labour.
The legitimisation of usury was the birth of capitalism.