6 Lend not money at interest. Thou accusest Scripture which says, “He that has not given his money upon usury.” I wrote not this: it went not forth first from my mouth: hear God. He replies: let not the clergy lend upon usury. Perchance he who speaks to you, lends not at interest: but if he do so lend, suppose that he does so lend; does He who speaks through him lend at interest? If he does what he enjoins you, and thou dost it not; you will go into the flame, he into the kingdom. If he does not what he enjoins you, and equally with you does evil deeds, and preaches duties which he does not; you will both equally go into the flames. The hay will burn; but “the word of the Lord abides for evermore.”...
Source: The Enarrations, or Expositions, on the Psalms (New Advent)