c. 370–419 · Jerome, Letters 55.2
Accordingly all such sins as theft, manslaughter, pillage, perjury, and the like can be repented of after they have been committed; and, however much interest may tempt him, conscience always smites the offender. It is only lust and sensual pleasure that in the very hour of penitence undergo once more the temptations of the past, the itch of the flesh, and the allurements of sin; so that the very thought which we bestow on the correction of such transgressions becomes in itself a new source of sin. Or to put the matter in a different light: other sins are outside of us; and whatever we do we do against others. But fornication defiles the fornicator both in conscience and body; and in accordance with the words of the Lord, “for this cause shall a man leave father and mother, and shall cleave to his wife; and they twain shall be one flesh,” he too becomes one body with a harlot and sins against his own body by making what is the temple of Christ the body of a harlot.