On Marriage and Concupiscence

The entire good, therefore, of the nuptial institution was effected in the case of these parents of Christ: there was offspring, there was faithfulness, there was the bond. As offspring, we recognise the Lord Jesus Himself; the fidelity, in that there was no adultery; the bond, because there was no divorce. [XII.] Only there was no nuptial cohabitation; because He who was to be without sin, and was sent not in sinful flesh, but in the likeness of sinful flesh, could not possibly have been made in sinful flesh itself without that shameful lust of the flesh which comes from sin, and without which He willed to be born, in order that He might teach us, that every one who is born of sexual intercourse is in fact sinful flesh, since that alone which was not born of such intercourse was not sinful flesh.

Nevertheless conjugal intercourse is not in itself sin, when it is had with the intention of producing children; because the mind's good-will leads the ensuing bodily pleasure, instead of following its lead; and the human choice is not distracted by the yoke of sin pressing upon it, inasmuch as the blow of the sin is rightly brought back to the purposes of procreation. This blow has a certain prurient activity which plays the king in the foul indulgences of adultery, and fornication, and lasciviousness, and uncleanness; while in the indispensable duties of the marriage state, it exhibits the docility of the slave.

In the one case it is condemned as the shameless effrontery of so violent a master; in the other, it gets modest praise as the honest service of so submissive an attendant. This lust, then, is not in itself the good of the nuptial institution; but it is obscenity in sinful men, a necessity in procreant parents, the fire of lascivious indulgences, the shame of nuptial pleasures. Wherefore, then, may not persons remain man and wife when they cease by mutual consent from cohabitation; seeing that Joseph and Mary continued such, though they never even began to cohabit?