A Kingdom Implies a King
The kingdom of God and the kingdom of heaven seem to be variations of the same idea. A kingdom implies a king. Our king is Jesus. Jesus said His kingdom was not of this world (John 18:36). Jesus authority did not come from man but from God (Luke 22:29).
Entrance into the kingdom of God is by a new birth (John 3:5), repentance (Matt. 3:2), and the divine call (1 Thess. 2:12). We are told to seek the kingdom of God first (Matt. 6:33) and to pray for its arrival (Matt. 6:10). “The kingdom of God is not eating and drinking, but righteousness and peace and joy in the Holy Spirit” (Rom. 14:17). It is also a future kingdom where full rulership in the actual presence of the king Jesus will occur when He returns to earth.
An expression first used by Jesus, although the idea that God reigns is everywhere in the Old Testament. The coming of the kingdom of God was the most frequent topic in the teaching of Jesus (Mark 1:15). It expresses the truth that God is a great God who does what he wills in human affairs. Specifically he wills to save people through the life, death, resurrection, and ascension of Jesus. In one sense the kingdom of God is a present reality. People enter it now (Matt. 21:31). In another sense it is future (Matt. 16:28). Gods control is plain in both aspects, and in the end his sovereign will will be perfectly done (1 Cor. 15:28).