17 These testimonies are sufficient for the believing who study truth, and the unbelieving credit no testimony. For the Holy Spirit, indeed, in the person of the apostles, has testified to this, saying, “And who has believed our report?” Therefore let us not prove ourselves unbelieving, lest the word spoken be fulfilled in us. Let us believe then, dear brethren, according to the tradition of the apostles, that God the Word came down from heaven, (and entered) into the holy Virgin Mary, in order that, taking the flesh from her, and assuming also a human, by which I mean a rational soul, and becoming thus all that man is with the exception of sin, He might save fallen man, and confer immortality on men who believe in His name.
In all, therefore, the word of truth is demonstrated to us, to wit, that the Father is One, whose word is present (with Him), by whom He made all things; whom also, as we have said above, the Father sent forth in later times for the salvation of men. This (Word) was preached by the law and the prophets as destined to come into the world. And even as He was preached then, in the same manner also did He come and manifest Himself, being by the Virgin and the Holy Spirit made a new man; for in that He had the heavenly (nature) of the Father, as the Word and the earthly (nature), as taking to Himself the flesh from the old Adam by the medium of the Virgin, He now, coming forth into the world, was manifested as God in a body, coming forth too as a perfect man.
For it was not in mere appearance or by conversion, but in truth, that He became man.
Source: Against the Heresy of Noetus (New Advent)