11 Nor do we ourselves set forth this in virgins, that they are virgins; but that they are virgins dedicated unto God by pious continence. For it is not at a venture that I may say, a married woman seems to me happier than a virgin about to be married: for the one has what the other as yet desires, especially if she be not yet even the betrothed of any one. The one studies to please one, unto whom she has been given; the other many, in doubt unto whom she is to be given: by this one thing she guards modesty of thought from the crowd, that she is seeking, not an adulterer, but a husband, in the crowd.
Therefore that virgin is with good reason set before a married woman, who neither sets herself forth for the multitude to love, whereas she seeks from out the multitude the love of one; nor, having now found him, orders herself for one, taking thought of the things of the world, “how to please her husband;” but has so loved “Him of fair beauty above the sons of men,” as that, because she could not, even as Mary, conceive Him in her flesh, she has kept her flesh also virgin for Him conceived in her heart.
This kind of virgins no fruitfulness of the body has given birth to: this is no progeny of flesh and blood. If of these the mother be sought for, it is the Church. None bears sacred virgins save a sacred virgin, she who has been espoused to be presented chaste unto one Husband, Christ. Of her, not altogether in body, but altogether in spirit virgin, are born holy virgins both in body and in spirit.
Source: On Holy Virginity (New Advent)