8 Whence, also, what the Apostle Paul said of the unmarried woman, “that she may be holy both in body and spirit;” we are not so to understand, as though a faithful woman being married and chaste, and according to the Scriptures subject unto her husband, be not holy in body, but only in spirit. For it cannot come to pass, that when the spirit is sanctified, the body also be not holy, of which the sanctified spirit makes use: but, that we seem not to any to argue rather than to prove this by divine saying; since the Apostle Peter, making mention of Sarah, says only “holy women,” and says not, “and in body;” let us consider that saying of the same Paul, where forbidding fornication he says, “Do you not know, that your bodies are members of Christ?
Taking, therefore, members of Christ, shall I make them members of an harlot? Far be it.” Therefore let any one dare to say that the members of Christ are not holy; or let him not dare to separate from the members of Christ the bodies of the faithful that are married. Whence, also, a little after he says, “Your body is the temple within you of the Holy Spirit, Whom you have from God; and you are not your own; for you have been bought with a great price.” He says that the body of the faithful is both members of Christ, and the temple of the Holy Spirit, wherein assuredly the faithful of both sexes are understood.
There therefore are married women, there unmarried women also; but distinct in their deserts, and as members preferred to members, while yet neither are separated from the body. Whereas, therefore, he says, speaking of an unmarried woman, “that she may be holy both in body and spirit,” he would have understood a fuller sanctification both in body and in spirit, and has not deprived the body of married women of all sanctification.
Source: On the Good of Widowhood (New Advent)