Nicene and Post-Nicene Fathers, Vol. III:
Moral Treatises of St. Augustin: Section 8

8. Therefore no fruitfulness of the flesh can be compared to holy virginity even of the flesh. For neither is itself also honored because it is virginity, but because it hath been dedicated to God, and, although it be kept in the flesh, yet is it kept by religion and devotion of the Spirit. And by this means even virginity of body is spiritual, which continence of piety vows and keeps. For, even as no one makes an immodest use of the body, unless the sin have been before conceived in the spirit, so no one keeps modesty in the body, unless chastity have been before implanted in the spirit. But, further, if modesty of married life, although it be guarded in the flesh, is yet attributed to the soul, not to the flesh, under the rule and guidance of which, the flesh itself hath no intercourse with any beside its own proper estate of marriage; how much more, and with how much greater honor, are we to reckon among the goods of the soul that continence, whereby the virgin purity of the flesh is vowed, consecrated, and kept, for the Creator Himself of the soul and flesh.