12 “You, Lord, shall recompense for me”. I recompense not: You shall recompense. Let mine enemies rage their full: You shall recompense what I cannot....“Dearly beloved, avenge not yourselves,” says the Apostle, “but rather give place unto wrath; for it is written, Vengeance is Mine, I will repay, says the Lord.” There is here another sense not to be neglected, perhaps even to be preferred. “Lord” Christ, “You shall repay for me.” For I, if I repay, have seized; You have paid what You have not seized.
Lord, You shall “repay for me.” Behold Him repaying for us. They came to Him, who exacted tribute: they used to demand as tribute a didrachma, that is, two drachmas for one man; they came to the Lord to pay tribute; or rather, not to Him, but to His disciples, and they said to them, “Does not your Master pay tribute?” They came and told Him. He says unto Peter, “lest we should offend them, go thou to the sea, and cast an hook, and take up the fish that first comes up: and when you have opened his mouth, you shall find a stater: that take, and give for Me and you.”
The first that rises from the sea, is the First-begotten from the dead. In His mouth we find two didrachmas, that is, four drachmas: in His mouth we find the four Gospels. By those four drachmas we are free from the claims of this world, by the four Evangelists we remain no longer debtors; for there the debt of all our sins is paid. He then has repaid for us, thanks to His mercy. He owed nothing: He repaid not for Himself: He repaid for us....
Source: The Enarrations, or Expositions, on the Psalms (New Advent)