6 So, again, if your exhortations to virginity resembled the teaching of the apostle, "He who gives in marriage does well, and he who gives not in marriage does better;" if you taught that marriage is good, and virginity better, as the Church teaches which is truly Christ's Church, you would not have been described in the Spirit's prediction as forbidding to marry. What a man forbids he makes evil; but a good thing may be placed second to a better thing without being forbidden.
Moreover, the only honorable kind of marriage, or marriage entered into for its proper and legitimate purpose, is precisely that you hate most. So, though you may not forbid sexual intercourse, you forbid marriage; for the peculiarity of marriage is, that it is not merely for the gratification of passion, but, as is written in the contract, for the procreation of children. And, though you allow many of your followers to retain their connection with you in spite of their refusal, or their inability, to obey you, you cannot deny that you make the prohibition.
The prohibition is part of your false doctrine, while the toleration is only for the interests of the society. And here we see the reason, which I have delayed till now to mention, for your making not the birth but only the death of Christ feigned and illusory. Death being the separation of the soul, that is, of the nature of your god, from the body which belongs to his enemies, for it is the work of the devil, you uphold and approve of it; and thus, according to your creed, it was meet that Christ, though He did not die, should commend death by appearing to die.
In birth, again, you believe your god to be bound instead of released; and so you will not allow that Christ was born even in this illusory fashion. You would have thought better of Mary had she ceased to be a virgin without being a mother, than as being a mother without ceasing to be a virgin. You see, then, that there is a great difference between exhorting to virginity as the better of two good things, and forbidding to marry by denouncing the true purpose of marriage; between abstaining from food as a symbolic observance, or for the mortification of the body, and abstaining from food which God has created for the reason that God did not create it. In one case, we have the doctrine of the prophets and apostles; in the other, the doctrine of lying devils.
Source: Reply to Faustus the Manichaean (New Advent)