On the Godhead
Since certainly “grace and truth came by Jesus Christ,” whence also by grace we are saved, according to that word of the apostle, “and that not of yourselves, nor of works, Jest any man should boast;” by the will of God, “the Word was made flesh,” and “was found in fashion as a man.” But yet He was not left without His divinity. For neither “though He was rich did He become poor” that He might absolutely be separated from His power and glory, but that He might Himself endure death for us sinners, the just for the unjust, that He might bring us to God, “being put to death in the flesh, but quickened by the Spirit;”and afterwards other things.
Whence the evangelist also asserts the truth when he says, “The Word was made flesh, and dwelt among us;”then indeed, from the time when the angel had saluted the virgin, saying, “Hail, you that are highly favoured, the Lord is with you.” Now when Gabriel said, “The Lord is with you,” he meant God the Word is with you. For he shows that He was conceived in the womb, and was to become flesh; as it is written, “The Holy Ghost shall come upon you, and the power of the Highest shall overshadow you; therefore also that holy thing which shall be born of you shall be called the Son of God;” and afterwards other things.
Now God the Word, in the absence of a man, by the will of God, who easily effects everything, was made flesh in the womb of the virgin, not requiring the operation of the presence of a man. For more efficacious than a man was the power of God overshadowing the virgin, together with the Holy Ghost also who came upon her.
Source: Fragments (New Advent)