Nicene and Post-Nicene Fathers, Ser. II, Vol. III:
Life and Works of Rufinus with Jerome's Apology Against Rufinus.: Section 12

12. But they say, perhaps, If it was possible to God that a virgin should conceive, it was possible also that she should bring forth, but they think it unmeet that a being of so great majesty should enter the world in such wise, that even though there had been no defilement from intercourse with man, there should yet be the unseemliness attendant upon the act of delivery. To which let us reply briefly, meeting them on their own level. If a person should see a little child in the act of being suffocated in a quagmire, and himself, a great man and powerful, should go into the mire, just at its verge, so to say, to rescue the dying child; would you blame this man as defiled for having stepped into a little mire, or would you praise him as merciful, for having preserved the life of one that was perishing? But the case supposed is that of an ordinary man. Let us return to the nature of Him Who was born. How much, think you, is the nature of the Sun inferior to him? How much beyond doubt, the Creature to the Creator? Consider now if a ray of the sun alights upon a quagmire, does it receive any pollution from it? or is the sun the worse for shedding his light upon foul objects? Fire, too, how far inferior is its nature to the things of which we are speaking? Yet no substance, whether foul or vile, is believed to pollute fire if applied to it. When the case is plainly thus with regard to material things, do you suppose that aught of pollution and defilement can befall that supereminent and incorporeal nature, which is above all fire and all light? Then, lastly, note this also: we say that man was created by God out of the clay of the earth. But if God is thought to be defiled in seeking to recover His own work, much more must He be thought so in making that work originally. And it is idle to ask why He passed through what is repugnant to our sense of modesty, when you cannot tell why He made what is so repugnant. And therefore it is not nature but general estimation that has made us think these things to be such. Otherwise, all things that are in the body, being formed from one and the same clay, are distinguished from one another only in their uses and natural offices.