From the Office of Readings for today, a discourse by Origen:
The coming of the kingdom of God, says our Lord and Saviour, does not admit of observation, and there will be no-one to say “Look here! Look there!” For the kingdom of God is within us and in our hearts. And so it is beyond doubt that whoever prays for the coming of the kingdom of God within himself is praying rightly, praying for the kingdom to dawn in him, bear fruit and reach perfection. For God reigns in every saint, and every saint obeys God’s spiritual laws — God, who dwells in him just as he dwells in any well-ordered city. The Father is present in him and in his soul Christ reigns alongside the Father, as it is said: We will come to him and make our dwelling with him.
Therefore, as we continue to move forward without ceasing, the kingdom of God within us will reach its perfection in us at that moment when the saying in the Apostle is fulfilled, that Christ, His enemies all made subject to Him, shall deliver the kingdom to God the Father that God may be All in All.
For this reason let us pray without ceasing, our souls filled by a desire made divine by the Word Himself. Let us pray to our Father in heaven: hallowed be thy name; thy kingdom come.
There is something important that we need to understand about the kingdom of God: just as righteousness has no partnership with lawlessness, just as light has nothing in common with darkness and Christ has no agreement with Belial, so the kingdom of God and a kingdom of sin cannot co-exist.
So if we want God to reign within us, on no account may sin rule in our mortal body but let us mortify our earthly bodies and let us be made fruitful by the Spirit. Then we will be a spiritual garden of Eden for God to walk in. God will rule in us with Christ who will be seated in us on the right hand of God — God, the spiritual power that we pray to receive — until he makes his enemies (who are within us) into his footstool and pours out on us all authority, all power, all strength.
This can happen to any one of us and death, the last enemy may be destroyed, so that in us Christ says Death, where is your sting? Death, where is your victory? So let our corruptibility be clothed today with holiness and incorruption. With Death dead, let our mortality be cloaked in the Father’s immortality. With God ruling in us, let us be immersed in the blessings of regeneration and resurrection.