By St. John Chrysostom
And so having beforehand prepared the hearer to look for some ordinary piece of information, and by this laying hold of him, after all he amazes him by adding the marvelous fact, saying, "Before they came together, she was found with child of the Holy Spirit..." (Matt. 1:18). Proceed therefore no further, neither require anything more than what has been said. Neither say, "But how was it that the Spirit wrought this of a virgin?" For if, when nature is at work, it is impossible to explain the manner of the formation; how, when the Spirit is working miracles, shall we be able to express these? And lest you should weary the evangelist, or disturb him by continually asking these things, he has said who it was that wrought the miracle, and so withdrawn himself. "For I know," says he, "nothing more, but that what was done was the work of the Holy Spirit."
Shame on them who busy themselves touching the generation on high. For if this birth, which has witnesses without number, and had been proclaimed so long a time before, and was manifested and handled with hands, can by no man be explained; of what excess of madness do they come short who make themselves busy and curious touching that unutterable generation? For neither Gabriel nor Matthew was able to say anything more, but only that it was of the Spirit; but how, of the Spirit, or in what manner, neither of them has explained; for neither was it possible.
Nor think that you have learned all, by hearing "of the Spirit." Nay, for we are ignorant of many things, even when we have learned this; as, for instance, how the Infinite is in a womb, how He that contains all things is carried, as unborn, by a woman; how the Virgin bears, and continues a virgin. How, I pray you, did the Spirit frame that Temple? How did He take not all the flesh from the womb, but a part thereof, and increased it, and fashioned it? For that He did come forth of the Virgin's flesh, He has declared by speaking of "that which was conceived in her" (Gal. 4:4); and Paul, by saying, "made of a woman;" whereby he stops the mouths of them that say, Christ came among us as through some channel. For, if this were so, what need of the womb? If this were so, He has nothing in common with us, but that flesh is of some other kind, and not of the mass which belongs to us. How then was He of the root of Jesse? How was He a rod? How Son of man? How was Mary His mother? How was He of David's seed? How did he "take the form of a servant" (Philip. 2:7)? how "was the Word made flesh" (Jn. 1:14)? and how says Paul to the Romans, "Of whom as concerning the flesh Christ came, who is God over all" (Rom. 9:5)? Therefore that He was of us, and of our substance, and of the Virgin's womb, is manifest from these things, and from others beside; but how, is not also manifest. Do not either then inquire; but receive what is revealed, and be not curious about what is kept secret.
From Homily on Matthew 4.6.