Marriage and Virginity
It seems to me, therefore, that at the present time the only ones who should marry are those who are unable to be continent, in accordance with that advice of the same apostle: If they are unable to be continent, they should marry; for it is better to marry than to burn (1 Cor 7:9).
11. In their case marriage is not a sin, although if it were chosen as an alternative to fornication, it would be less of a sin than the fornication, but it would still be a sin. Now, however, what are we to say in the face of the clear words of the apostle? He says, Let him do as he chooses; if he marries, he does not commit a sin (1 Cor 7:36), and, If you have married, you have not committed a sin, and if a virgin marries, she does not commit a sin (1 Cor 7:28).
It clearly follows from this that it is wrong to have any doubt about the sinlessness of marriage. Therefore, it is not marriage that the apostle allows as excusable; for who fails to see the absurdity of saying that persons are excused when they have not done anything wrong? Rather, what he allows as excusable is sexual intercourse that occurs because of a lack of self-control, not solely for the purpose of having children and sometimes not for the purpose of having children at all. Marriage does not make this happen, but it wins forgiveness for it. It must not be so excessive that it encroaches on time that should be set aside for prayer,†25 and it must not degenerate into the unnatural practice, about which the apostle could not remain silent, when he spoke about the depraved conduct of impure and immoral persons.†26 Sexual union that is necessary for the purpose of having children is blameless, and it alone is part of marriage. If it goes beyond that necessity, it is no longer ruled by reason but by sensuality. Nevertheless, it is proper for married persons to accord this to their spouses, so that the spouses will not commit a mortal sin of adultery, though it is not proper to require it for themselves. If they are both overcome by this kind of sensuality, clearly they are not doing something that is part of marriage. Nevertheless, if in their intimacy they value what is honorable more than what is dishonorable, that is to say, what is part of marriage rather than what is not part of marriage, then on the authority of the apostle this is allowed to them as something excusable. Marriage does not encourage this fault, but it pleads for it. They must not turn away God's mercy, either by failing to abstain on certain days in order to be free for prayer and to support their prayers with this abstinence in the same way as one does by fasting, or by transforming the natural practice into that unnatural practice, which is even more deserving of damnation when it is done with one's spouse.
Unnatural Sexual Relations and Marital Holiness