“Then shall Christ hand over the Kingdom to his Father,” Saint Paul says (1Cor 15,24), not in the sense that he will yield up his power by handing the Kingdom over to him, but because we ourselves will be God's Kingdom when we have been conformed to the glory of his body..., constituted Kingdom of God through the glorification of his body. It is we who he will hand over as Kingdom to the Father, as it is written in the Gospel: “Come, you who are blessed by my Father, inherit the Kingdom prepared for you from the foundation of the world” (Mt 25,34).
“Then shall the just shine out like the sun in the Kingdom of their Father”. For the Son will hand over to the Father as his Kingdom those he has invited into his Kingdom, those to whom he has promised the blessedness proper to this mystery in the words: “Blessed are the pure in heart for they shall see God” (Mt 5,8)... See how those whom he hands over to his Father, as being his Kingdom, see God.
Our Lord himself made known to his apostles in what this Kingdom consists: “The Kingdom of God is among you” (Lk 17,21). And if anyone wants to know who it is who hands over the Kingdom, let him hear: “Christ has been raised from the dead, the firstfruits of those who have fallen asleep. For since death came through a human being, the resurrection of the dead came also through a human being” (1Cor 15,20-21). All this concerns the mystery of the Body since Christ was the first to be raised from the dead... So it is for the development of the humanity that Christ assumed that “God will be all in all” (1Cor 15,28).
Saint Hilary (c.315-367), Bishop of Poitiers, Doctor of the Church