God’s kingdom is His sovereign rule over all things (Psalm 103:19). The OT prophets spoke of a future where God’s sovereign rule through the Messiah would be recognized by all nations (Psalm 2:6; Daniel 7:14-15). The Messiah will rule in order to bring redemption to His elect in all nations and to destroy all who oppose redemption (Psalm 110).
ALREADY AND NOT YET
The NT opens with John the Baptist’s announcement, “Repent, for the kingdom of heaven is at hand” (Matthew 3:2). This means the kingdom is near, about to burst onto the scene. Just a short time later, Christ came preaching the same message, “The time is fulfilled, the kingdom of God is at hand; repent and believe the gospel” (Mark 1:15). Notice: the terms kingdom of God and kingdom of heaven are used interchangeably, showing they refer to the same thing.
When the Pharisees asked Jesus when the kingdom of God would come, Jesus replied, “Behold, the kingdom of God is in the midst of you” (Luke 17:21). The kingdom was in their midst because the King was there. On another occasion, Jesus said, “But if it is by the finger of God that I cast out demons, then the kingdom of God has come upon you” (Luke 11:20).
Many of Jesus’ parables begin, “The kingdom of God is like…” The parables make it clear that the kingdom has a progressive character. The kingdom started small, but over time it began to expand, and it will continue to grow until it encompasses all things. Jesus said that the kingdom is like a mustard seed, the smallest of seeds (Matt. 13:31-22). He also compared it to leaven, which spreads through the dough so that the lump enlarges (Matt. 13:33). The OT foretold that the kingdom would fill the earth (Daniel 2:35, 44).
CHRIST REIGNS NOW
After Christ died on the cross for His chosen people, He rose from the dead, and ascended into heaven to go to his coronation, where God declared Him King (Acts 2:32-36). Christ has inaugurated the kingdom of God. Christ reigns now as the Lamb of God who is worthy to receive the kingdom. The kingdom is growing, as more people believe in Christ, but it will not be consummated until Christ comes at the end of history to subdue all kingdoms. The prayer, “Your kingdom come,” is a prayer for the kingdom to come more and more until it comes in all its fullness (cf. Heidelberg Catechism, Q&A 123).
It is the fundamental mission of the church to bear witness to the kingdom of God (as Paul did in Acts 28:31). Jesus made it clear that we, as His disciples, are to “seek first the kingdom of God” (Matt. 6:33; cf. Rom. 14:17). According to Jesus, seeking the kingdom is the most important task of the Christian life.
[Adapted from R.C. Sproul, Everyone’s a Theologian]