7 I have said this, lest haply married fruitfulness dare to vie with virgin chastity, and to set forth Mary herself, and to say unto the virgins of God, She had in her flesh two things worthy of honor, virginity and fruitfulness; inasmuch as she both continued a virgin, and bore: this happiness, since we could not both have the whole, we have divided, that you be virgins, we be mothers: for what is wanting to you in children, let your virginity, that has been preserved, be a consolation: for us, let the gain of children make up for our lost virginity.
This speech of faithful women married, unto holy virgins, would any how be to be endured, if they gave birth to Christians in the flesh; that in this alone, save virginity, the fruitfulness of Mary in the flesh should be more excellent, that she gave birth to the Head Himself of these members, but they to the members of That Head: but now, although by this speech there vie such as on this one account wed and have intercourse with husbands, that they may have sons, and have no other thought of their sons, than to gain them for Christ, and do this so soon as they can: yet are not Christians born of their flesh, but made so afterwards: the Church giving them birth, through this, that in a spiritual manner she is the mother of the members of Christ, of Whom also after a spiritual manner she is the virgin.
And unto this holy birth mothers also who have not borne in the flesh Christians, are workers together, that they may become what they know that they could not give birth to in the flesh: yet are they workers together through this, wherein themselves also are virgins and mothers of Christ, that is to say, in “faith which works through love.”
Source: On Holy Virginity (New Advent)