Reply Obj. 1: Christ is said in two ways to have come down from heaven. First, as regards His Divine Nature; not indeed that the Divine Nature ceased to be in heaven, but inasmuch as He began to be here below in a new way, viz. by His assumed nature, according to John 3:13: "No man hath ascended into heaven, but He that descended from heaven, the Son of Man, Who is in heaven."
Secondly, as regards His body, not indeed that the very substance of the body of Christ descended from heaven, but that His body was formed by a heavenly power, i.e. by the Holy Ghost. Hence Augustine, explaining the passage quoted, says (Ad Orosium [*Dial. Qq. lxv, qu. 4, work of an unknown author]): "I call Christ a heavenly man because He was not conceived of human seed." And Hilary expounds it in the same way (De Trin. x).
Reply Obj. 2: Flesh and blood are not taken here for the substance of flesh and blood, but for the corruption of flesh, which was not in Christ as far as it was sinful; but as far as it was a punishment; thus, for a time, it was in Christ, that He might carry through the work of our redemption.
Reply Obj. 3: It pertains to the greatest glory of God to have raised a weak and earthly body to such sublimity. Hence in the General Council of Ephesus (P. II, Act. I) we read the saying of St. Theophilus: "Just as the best workmen are esteemed not merely for displaying their skill in precious materials, but very often because by making use of the poorest clay and commonest earth, they show the power of their craft; so the best of all workmen, the Word of God, did not come down to us by taking a heavenly body of some most precious matter, but shewed the greatness of His skill in clay." _______________________
THIRD ARTICLE [III, Q. 5, Art. 3]
Whether the Son of God Assumed a Soul?
Objection 1: It would seem that the Son of God did not assume a soul. For John has said, teaching the mystery of the Incarnation (John 1:14): "The Word was made flesh"—no mention being made of a soul. Now it is not said that "the Word was made flesh" as if changed to flesh, but because He assumed flesh. Therefore He seems not to have assumed a soul.
Obj. 2: Further, a soul is necessary to the body, in order to quicken it. But this was not necessary for the body of Christ, as it would seem, for of the Word of God it is written (Ps. 35:10): Lord, "with Thee is the fountain of life." Therefore it would seem altogether superfluous for the soul to be there, when the Word was present. But "God and nature do nothing uselessly," as the Philosopher says (De Coel. i, 32; ii, 56). Therefore the Word would seem not to have assumed a soul.
Obj. 3: Further, by the union of soul and body is constituted the
common nature, which is the human species. But "in the Lord Jesus
Christ we are not to look for a common species," as Damascene says
(De Fide Orth. iii, 3). Therefore He did not assume a soul.
On the contrary, Augustine says (De Agone Christ. xxi): "Let us not hearken to such as say that only a human body was assumed by the Word of God; and take 'the Word was made flesh' to mean that the man had no soul nor any other part of a man, save flesh."