Why does the Creed say that “his kingdom shall have no end?”
By this expression, the Creed adopts the very words of Gabriel to the Theotokos at the Annunciation, “the Lord God will give him the throne of his father David, and he will reign over the house of Jacob forever; and of his Kingdom there shall be no end” (Luk 1:32–33; see Q043, Q176), and refutes the notion (advanced by Marcellus of Ancyra in the fourth century) that the kingdom of Christ is only a temporary arrangement. The Church does not consider this teaching inconsistent with the words of St Paul:
When the end comes, he will deliver the Kingdom to the God and Father… he must reign until he has put all his enemies under his feet. The last enemy to be abolished is death… When all things have been subjected to him, then the Son will also subject himself to the One who subjected all things to him, so that God may be all in all (1Co 15:24–28).
The “delivering up” of the Kingdom is not its ending, but its consummation, the one eternal Kingdom of the Father, the Son, and the Holy Spirit, in which the redeemed “will reign forever and ever” (Rev 22:5; see Q236).