33 Thus St. John the Evangelist declares: 'The Word was made flesh' ( John i, 14). St. Paul writes of him: 'When he was in the form of God . . . he humbled himself and became obedient even unto death' ( Phil . ii, 6-8); or again: 'But when the fullness of time was come, God sent his Son, made from a woman' ( Gal . iv, 4), and our Divine Redeemer himself put the matter beyond doubt when he says: 'I and the Father are One' ( John x, 30); and again, 'I went out from the Father and I came into the world' John xvi, 28). The divine origin of our Redeemer is also manifest from this passage of the Gospel: 'I came down from heaven, not that I should do my own will, but the will of him that sent me' ( John vi, 38). And again: 'He who descended, this is he who ascended above all the heavens' ( Eph . iv, 10). St. Thomas Aquinas explains this last sentence thus: 'He who descended, this is the same as he who ascended. By these words is signified the unity of the person of God and man. For the Son of God came down by taking human nature, but the Son of Man ascended according to his human nature to the sublimity of eternal life. And so he is the same Son of God who came down and Son of Man who went up' (St. Thomas, Comm. in Ep. ad Eph. c iv. lect. iii circa finem ).
Source: Sempiternus Rex Christus (Vatican.va)