Deep study
The reign of God - already here, not yet complete
Jesus' very first message was, the kingdom of God is at hand. Grasping the kingdom unlocks the whole of the Gospels.
The kingdom of God is first of all God's reign - His kingly rule breaking into the world to save - and only secondarily a realm or place. The Greek basileia points to the activity of God ruling as King. So the kingdom is not mainly a where but a what: God acting, in power and mercy, to set things right.
Daniel saw one like a son of man come to the Ancient of Days and receive dominion and glory and a kingdom... an everlasting dominion that shall not pass away (Daniel 7:13-14). It is no accident that Son of Man became Jesus' favorite title for Himself: He was quietly claiming that everlasting kingdom as His own.
Jesus begins, the time is fulfilled, and the kingdom of God is at hand; repent and believe (Mark 1:15). His healings, His casting out of demons, His forgiving of sins, His raising of the dead - these are signs that the King has arrived and the powers of the age to come are spilling into the present.
The kingdom is both present and future. Jesus says the kingdom of God is in your midst (Luke 17:21), yet teaches us to pray, your kingdom come (Matthew 6:10). We live in the overlap - the King has come and reigns, but His reign is not yet visibly complete. The parables describe a kingdom that starts hidden and small - a mustard seed, leaven in dough - and grows to something vast. What looks unimpressive now will fill the earth.
You do not achieve your way into the kingdom; you receive it. Jesus' first command is repent and believe (Mark 1:15) - a turning of the whole self toward the King. He tells Nicodemus, unless one is born again he cannot see the kingdom of God (John 3:3): entry requires a new birth God alone gives. And He warns that unless you turn and become like children, you will never enter (Matthew 18:3), for the kingdom belongs to the poor in spirit (Matthew 5:3). The door is low; only the humble and dependent stoop through it. The Beatitudes are the kingdom's upside-down charter, blessing the very people the world overlooks.
The Sermon on the Mount sketches what life looks like where God reigns: enemies loved, debts forgiven, anxiety surrendered, treasure stored in heaven. Greatness is redefined - whoever would be great among you must be your servant (Mark 10:43) - because the King Himself came not to be served but to serve. Seek first the kingdom of God and his righteousness, Jesus says, and all these things will be added (Matthew 6:33). The church is meant to be the present colony of that kingdom: an outpost where the future reign of God is already visible in how a people live together now.
The kingdom does not advance the way empires do. When the crowd tries to make Him king by force, Jesus withdraws (John 6:15); He enters Jerusalem not on a war-horse but on a donkey (Zechariah 9:9). He is crowned with thorns, and the charge nailed above Him reads, the King of the Jews (John 19:19) - a mockery that tells the truth. Before Pilate He says, my kingdom is not of this world (John 18:36); if it were, His servants would fight. This King conquers by dying and rising, and His kingdom spreads not by the sword but by the gospel and the cross-shaped lives of His people. We have been transferred into the kingdom of His beloved Son (Colossians 1:13).
The crucified and risen King already holds all authority in heaven and on earth (Matthew 28:18). And the story ends with the seventh trumpet and a shout: The kingdom of the world has become the kingdom of our Lord and of his Christ, and he shall reign forever and ever (Revelation 11:15).
The last scene of the Bible is a throne. The throne of God and of the Lamb stands at the center of a renewed creation; His servants worship Him, they see His face, and they reign with Him forever (Revelation 22:1-5). The prayer your kingdom come is finally and fully answered.