20 I praise wedlock, I praise marriage, but it is because they give me virgins. I gather the rose from the thorns, the gold from the earth, the pearl from the shell. “Does the plowman plow all day to sow?” Shall he not also enjoy the fruit of his labor? Wedlock is the more honored, the more what is born of it is loved. Why, mother, do you grudge your daughter her virginity? She has been reared on your milk, she has come from your womb, she has grown up in your bosom.
Your watchful affection has kept her a virgin. Are you angry with her because she chooses to be a king's wife and not a soldier's? She has conferred on you a high privilege; you are now the mother-in-law of God. “Concerning virgins,” says the apostle, “I have no commandment of the Lord.” Why was this? Because his own virginity was due, not to a command, but to his free choice. For they are not to be heard who feign him to have had a wife; for, when he is discussing continence and commending perpetual chastity, he uses the words, “I would that all men were even as I myself.”
And farther on, “I say, therefore, to the unmarried and widows, it is good for them if they abide even as I.” And in another place, “have we not power to lead about wives even as the rest of the apostles?” Why then has he no commandment from the Lord concerning virginity? Because what is freely offered is worth more than what is extorted by force, and to command virginity would have been to abrogate wedlock. It would have been a hard enactment to compel opposition to nature and to extort from men the angelic life; and not only so, it would have been to condemn what is a divine ordinance.
Source: Letters (New Advent)