Reply Obj. 1: These utterances were spoken prophetically of God who was one day to become incarnate. Still it can be said that although to ascend does not belong to the Divine Nature properly, yet it can metaphorically; as, for instance, it is said "to ascend in the heart of man" (cf. Ps. 83:6), when his heart submits and humbles itself before God: and in the same way God is said to ascend metaphorically with regard to every creature, since He subjects it to Himself.
Reply Obj. 2: He who ascended is the same as He who descended. For Augustine says (De Symb. iv): "Who is it that descends? The God-Man. Who is it that ascends? The self-same God-Man." Nevertheless a twofold descent is attributed to Christ; one, whereby He is said to have descended from heaven, which is attributed to the God-Man according as He is God: for He is not to be understood as having descended by any local movement, but as having "emptied Himself," since "when He was in the form of God He took the form of a servant." For just as He is said to be emptied, not by losing His fulness, but because He took our littleness upon Himself, so likewise He is said to have descended from heaven, not that He deserted heaven, but because He assumed human nature in unity of person.
And there is another descent whereby He descended "into the lower regions of the earth," as is written Eph. 4:9; and this is local descent: hence this belongs to Christ according to the condition of human nature.
Reply Obj. 3: Christ is said to ascend to the Father, inasmuch as He ascends to sit on the right hand of the Father; and this is befitting Christ in a measure according to His Divine Nature, and in a measure according to His human nature, as will be said later (Q. 58, A. 3). _______________________
THIRD ARTICLE [III, Q. 57, Art. 3]
Whether Christ Ascended by His Own Power?
Objection 1: It would seem that Christ did not ascend by His own power, because it is written (Mk. 16:19) that "the Lord Jesus, after He had spoken to them, was taken up to heaven"; and (Acts 1:9) that, "while they looked on, He was raised up, and a cloud received Him out of their sight." But what is taken up, and lifted up, appears to be moved by another. Consequently, it was not by His own power, but by another's that Christ was taken up into heaven.
Obj. 2: Further, Christ's was an earthly body, like to ours. But it is contrary to the nature of an earthly body to be borne upwards. Moreover, what is moved contrary to its nature is nowise moved by its own power. Therefore Christ did not ascend to heaven by His own power.
Obj. 3: Further, Christ's own power is Divine. But this motion does not seem to have been Divine, because, whereas the Divine power is infinite, such motion would be instantaneous; consequently, He would not have been uplifted to heaven "while" the disciples "looked on," as is stated in Acts 1:9. Therefore, it seems that Christ did not ascend to heaven by His own power.
On the contrary, It is written (Isa. 63:1): "This beautiful one in his robe, walking in the greatness of his strength." Also Gregory says in a Homily on the Ascension (xxix): "It is to be noted that we read of Elias having ascended in a chariot, that it might be shown that one who was mere man needed another's help. But we do not read of our Saviour being lifted up either in a chariot or by angels, because He who had made all things was taken up above all things by His own power."