Has this Kingdom not already come?

The Church prays, in the Divine Liturgy of St John Chrysostom, in a striking past tense: “You did not cease doing all things until You had led us up to heaven, and granted us Your Kingdom which is to come” (Anaphora). For the Reign of God has already been revealed, and the children of the Kingdom (Mat 13:38) already enjoy a foretaste of it, through the anointing of the Holy Spirit and the vision of “the glory of God in the face of Jesus Christ” (2Co 4:6). As St Basil writes:

Through the Holy Spirit comes our restoration to paradise, our ascension into the kingdom of heaven, our return to the adoption of sons, our liberty to call God our Father, our being made partakers of the grace of Christ, our being called children of light, our sharing in eternal glory, in a word, our being brought into a state of all fullness of blessing, both in this age and in the age to come. (St Basil the Great, On the Holy Spirit, 15.36)

As the Lord announced:

Amen, I tell you: there are some standing here who will not taste death until they see that the kingdom of God has come with power. Six days later, Jesus took with him Peter and James and John, and led them up a high mountain apart, by themselves; and he was transfigured before them. (Mrk 9:1–2)

Yet, as long as sin is allowed dominion in our mortal bodies, grieving the life of the Spirit, the Reign of God has not yet fully come, as St Paul admonishes: “do not let sin rule in your mortal body, that you should obey it in its lusts” (Rom 6:12).