32 Therefore the good of marriage throughout all nations and all men stands in the occasion of begetting, and faith of chastity: but, so far as pertains unto the People of God, also in the sanctity of the Sacrament, by reason of which it is unlawful for one who leaves her husband, even when she has been put away, to be married to another, so long as her husband lives, no not even for the sake of bearing children: and, whereas this is the alone cause, wherefore marriage takes place, not even where that very thing, wherefore it takes place, follows not, is the marriage bond loosed, save by the death of the husband or wife.
In like manner as if there take place an ordination of clergy in order to form a congregation of people, although the congregation of people follow not, yet there remains in the ordained persons the Sacrament of Ordination; and if, for any fault, any be removed from his office, he will not be without the Sacrament of the Lord once for all set upon him, albeit continuing unto condemnation. Therefore that marriage takes place for the sake of begetting children, the Apostle is a witness thus, “I will,” says he, “that the younger women be married.”
And, as though it were said to him, For what purpose? Straightway he added, “to have children, to be mothers of families.” But unto the faith of chastity pertains that saying, “The wife has not power of her own body, but the husband: likewise also the husband has not power of his own body, but the wife.” But unto the sanctity of the Sacrament that saying, “The wife not to depart from her husband, but, in case she shall have departed, to remain unmarried, or to be reconciled to her husband: and let not the husband put away his wife.” All these are goods, on account of which marriage is a good; offspring, faith, sacrament.
But now, at this time, not to seek offspring after the flesh, and by this means to maintain a certain perpetual freedom from every such work, and to be made subject after a spiritual manner unto one Husband Christ, is assuredly better and holier; provided, that is, men so use that freedom, as it is written, so as to have their thoughts of the things of the Lord, how to please the Lord; that is, that Continence at all times do take thought, that obedience fall not short in any matter: and this virtue, as the root-virtue, and (as it is wont to be called) the womb, and clearly universal, the holy fathers of old exercised in deed; but that Continence they possessed in habit of mind.
Who assuredly, through that obedience, whereby they were just and holy, and ever prepared unto every good work, even if they were bidden to abstain from all sexual intercourse, would perform it. For how much more easily could they, at the bidding or exhortation of God, not use sexual intercourse, who, as an act of obedience, could slay the child, for the begetting of which alone they used the ministry of sexual intercourse?
Source: On the Good of Marriage (New Advent)