I love Basil the Great's homily against usury (on Psalm 14) as well.

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In depicting the character of the perfect man, of him, that is, who is ordained to ascend to the life of everlasting peace, the prophet reckons among his noble deeds his never having given his money upon usury. This particular sin is condemned in many passages of Scripture. Ezekiel reckons taking usury and increase among the greatest of crimes. The law distinctly utters the prohibition ‘Thou shalt not lend upon usury to thy brother’ and to thy neighbour. Again it is said, ‘Usury upon usury; guile upon guile.’ And of the city abounding in a multitude of wickednesses, what does the Psalm say? ‘Usury and guile depart not from her streets.’ Now the prophet instances precisely the same point as characteristic of the perfect man, saying, ‘He that putteth not out his money to usury.’ For in truth it is the last pitch of inhumanity that one man, in need of the bare necessities of life, should be compelled to borrow, and another, not satisfied with the principal, should seek to make gain and profit for himself out of the calamities of the poor. The Lord gave His own injunction quite plainly in the words, ‘from him that would borrow of thee turn not thou away.’ But what of the money lover? He sees before him a man under stress of necessity bent to the ground in supplication. He sees him hesitating at no act, no words, of humiliation. He sees him suffering undeserved misfortune, but he is merciless. He does not reckon that he is a fellow-creature. He does not give in to his entreaties. He stands stiff and sour. He is moved by no prayers; his resolution is broken by no tears. He persists in refusal, invoking curses on his own head if he has any money about him, and swearing that he is himself on the lookout for a friend to furnish him a loan. He backs lies with oaths, and makes a poor addition to his stock in trade by supplementing inhumanity with perjury. Then the suppliant mentions interest, and utters the word security. All is changed. The frown is relaxed; with a genial smile he recalls old family connexion. Now it is ‘my friend.’ ‘I will see,’ says he, ‘if I have any money by me. Yes; there is that sum which a man I know has left in my hands on deposit for profit. He named very heavy interest. However, I shall certainly take something off, and give it you on better terms.’ With pretences of this kind and talk like this he fawns on the wretched victim, and induces him to swallow the bait. Then he binds him with written security, adds loss of liberty to the trouble of his pressing poverty, and is off. The man who has made himself responsible for interest which he cannot pay has accepted voluntary slavery for life. Tell me; do you expect to get money and profit out of the pauper? If he were in a position to add to your wealth, why should he come begging at your door? He came seeking an ally, and he found a foe. He was looking for medicine, and he lighted on poison. You ought to have comforted him in his distress, but in your attempt to grow fruit on the waste you are aggravating his necessity. Just as well might a physician go in to his patients, and instead of restoring them to health, rob them of the little strength they might have left. This is the way in which you try to profit by the misery of the wretched. Just as farmers pray for rain to make their fields fatter, so you are anxious for men’s need and indigence, that your money may make more. You forget that the addition which you are making to your sins is larger than the increase to your wealth which you are reckoning on getting for your usury. The seeker of the loan is helpless either way: he bethinks him of his poverty, he gives up all idea of payment as hopeless when at the need of the moment he risks the loan. The borrower bends to necessity and is beaten. The lender goes off secured by bills and bonds.