31 He Ascended into Heaven, and Sits on the Right Hand of the Father: from Thence He Shall Come to Judge the Quick and the Dead. These clauses follow with suitable brevity at the end of this part of the Creed which treats of the Son. What is said is plain, but the question is how and in what sense it is to be understood. For to “ascend,” and to “sit,” and to “come,” unless you understand the words in accordance with the dignity of the divine nature, appear to point to something of human weakness.
For having consummated what was to be done on earth, and having recalled souls from the captivity of hell, He is spoken of as ascending up to heaven, as the Prophet had foretold, “Ascending up on high He led captivity captive, and gave gifts unto men,” those gifts, namely, which Peter, in the Acts of the Apostles, spoke of concerning the Holy Ghost, “Being therefore by the right hand of God exalted, He has shed forth this gift which you do see and hear.” He gave the gift of the Holy Ghost to men, because the captives, whom the devil had before carried into hell through sin, Christ by His resurrection from death recalled to heaven.
He ascended therefore into heaven, not where God the Word had not been before, for He was always in heaven, and abode in the Father, but where the Word made flesh had not been seated before. Lastly, since this entrance within the gates of heaven seemed new to its ministers and princes, they say to one another, on seeing the nature of flesh penetrating into the secret recesses of heaven, as David full of the Holy Ghost, declares, “Lift up your gates, you princes, and be lifted up ye everlasting gates, and the King of glory shall enter in.
Who is the King of glory? The Lord strong and mighty, the Lord mighty in battle.” Which words are spoken not with reference to the power of the divine nature, but with reference to the novelty of flesh ascending to the right hand of God. The same David says elsewhere, “God has ascended jubilantly, and the Lord with the sound of the trumpet.” For conquerors are wont to return from battle with the sound of the trumpet. Of Him also it is said, “Who builds up His ascent in heaven.” And again, “Who has ascended above the cherubims, flying upon the wings of the winds.”
Source: Commentary on the Apostles' Creed (New Advent)