Thomas Aquinas — on 1Cor 7:2 (Commentary on 1 Corinthians)

“Then when he says, But because of fornication, he shows what is necessary in this matter: first, as to contracting marriage; secondly, as to the use of the matrimony once contracted (v. 3). In regard to the first it should be noted that the act of the generative power is ordained to the conservation of the species by the generation of offspring. And because the woman was given to the man as a helper in generation, the first need for touching a woman is for the procreation of children. Hence it says in Genesis (1:27): "Male and female he created them. And God blessed them, and God said to them, 'Be fruitful and multiply, and fill the earth.'" But this need was directed to the formation of the human race, as long as there was need for the people of God to be multiplied by succession according to the flesh. But the Apostle, considering that the human race had now multiplied and that the people of God were now increased not by fleshly propagation but by the generation which is from water the Holy Spirit, as it says in Jn (3:5), he passed over this necessity whereby marriage had been originally instituted as a function of nature, and proposed a second necessity according to which it was instituted as a remedy for sin. For since carnal desire remains alive in believers even after baptism, although it does not rule, it impels men especially toward venereal acts on account of the vehemence of their pleasure. And because it requires greater virtue to conquer this desire entirely than can belong to men, according to Matthew (19:11): "Not all men can receive this saying", it is necessary that this desire be in part yielded to and in part mastered. This, indeed, happens when the act of generation is ordained by reason and man is not totally mastered by the desire, but the desire is rather subjected to reason. Natural reason teaches that man use the act of generation according as it is suitable for generation and education of children. But in brute animals it is found that in certain species the female alone is not sufficient for the training of the offspring, but the male takes care of the offspring with the female. For this it is required that the male recognize its offspring. Therefore, in all such animals, as doves, pigeons and the like, solicitude for the training of offspring is inspired by nature. Wherefore, in such animals coition is not random and indiscriminate, but a definite male is joined to a definite female, not one to another promiscuously, as happens in dogs and such animals, in which the female alone takes care of the offspring. But above all in the human species, the male is required for the education of the offspring, which are attended to not only regarding bodily nourishment, but to a greater degree regarding the nourishment of the soul, as it says in Hebrews (12:9): "We have had earthly fathers to discipline us and we respected them." And consequently, natural reason dictates that in the human species coition is not random and uncertain, but is by a definite man to a definite female, who in fact made the arrangement through the law of matrimony. Thus, therefore, matrimony has three goods. The first is that it is a function of nature in the sense that it is ordered to the production and education of offspring; and this good is the good of offspring. The second good is that it is a remedy for desire, which is restricted to a definite person; and this good is called fidelity, which a man preserves toward his wife, by not going to another woman, and similarly the wife toward the husband. The third good is called the sacrament, inasmuch as it signifies the union of Christ and the Church, as it says in Ephesians (5:32): "This mystery [sacrament] is a profound one, and I am saying that it refers to Christ and the church." This therefore is what he says. It has been stated that, it is good for a man not to touch a woman. But because all men are not equipped for this good, each man on account of the temptation to fornication should have his own wife, that is, determined by himself, so as to avoid uncertain and promiscuous concubinage, which pertains to fornication: "Rejoice in the wife of your youth" (Prov. 5:18); "Why should you be infatuated, my son with a loose woman" (Prov. 5:20).”