Jesus’ message though simple was eternally far reaching. So when begins with “Repent for the Kingdom of heaven is at hand” he is announcing the fulfillment of the prophecy in Genesis 3:15, “And I will put enmity between you and the woman, and between your seed and her seed; He shall bruise you on the head, and you shall bruise him on the heel.”
The Kingdom of Heaven is described by the Baker Encyclopedia of the Bible* as, “The sovereign rule of God, initiated by Christ’s earthly ministry and to be consummated when “the kingdom of the world has become the kingdom of our Lord and of his Christ” (Rev 11:15).
Here is an extended definition of the Kingdom provided by the “Dictionary of Theological Terms”**.
What the Kingdom Is
The rule of God through His Son. God’s kingdom is the kingdom of heaven because it is heavenly in its origin and authority. But the sphere and realization of its rule have to do largely with the earth. Thus it confronts men here on earth with the message that the King Himself has come into the world, preaching repentance and submission to His kingly authority. Those who accept this gracious gospel of the kingdom (Acts 20:24, 25) will at once enter into eternal life and will forever enjoy the security and ecstacy of eternal glory (Matt. 8:11–12; 25:34).
The Kingdom Is Present
It Came with Christ. The NT speaks of the kingdom as coming with Christ. It is the kingdom of God’s dear Son (Col. 1:13). It is now present (Matt. 12:28; Luke 17:21, where within you means “in the midst of you”).
The Kingdom and Eternal Life. Kingdom of heaven is also a synonym for eternal life (Matt. 19:16, 23). It demands a response of repentance as the only way of entrance (Matt. 4:17). The preaching of the kingdom is the preaching of the gospel of grace (Acts 20:24, 25) promising all who repent and receive Christ an immediate place in God’s kingdom.
The Kingdom and the Church. It is clear that the kingdom and the church are closely related. In Matt. 16:16, 18–19 Jesus speaks to Peter about building His church and proceeds at once to promise him the keys of the kingdom. While kingdom and church are not altogether synonymous, they stand in a special closeness. The kingdom is the mediatorial rule of Christ and the sphere in which He exercises that rule. The church is the fellowship of the people who have received the offer of the kingdom. So, kingdom emphasizes Christ’s gracious sovereignty, and church emphasizes His redeemed people.
The Kingdom Is Future
It Will Come with Christ. The dying thief asked the Lord, “Remember me when thou comest into thy kingdom” (Luke 23:42), and the Saviour immediately assured him of a place in paradise (v. 43). But the thief’s words indicate that he was anticipating a future kingly reign for Christ. He was not mistaken, for while the kingdom is in one sense present, in another it is still future. We pray, “Thy kingdom come” (Matt. 6:10). Paul looked forward to Christ’s “appearing and his kingdom” and rejoiced that the Lord “will preserve me unto his heavenly kingdom” (2 Tim. 4:1, 18).
Living in the Light of the Kingdom to Come. The Sermon on the Mount (Matt. 5–7) and the various parables of the kingdom Jesus told (Matt. 13, 25) speak of the personal and corporate development of the people of God on earth in submission to the kingship of Christ. These passages deal with the deep ethical, evangelical, and eschatological issues that arise as the gospel confronts men and calls them to Christ. They show that the kingdom is both a present and future kingdom of messianic, or mediatorial, grace.
The Eternal Kingdom. The kingdom is “the everlasting kingdom of our Lord and Saviour Jesus Christ” (2 Peter 1:11). Its full and eternal expression will come when all things are finally summed up in Christ the head (Eph. 1:10) and all other authority and power have been put down never to rise again (1 Cor. 15:24, 25).**
*Elwell, W. A., & Beitzel, B. J. (1988). In Baker encyclopedia of the Bible (p. 1269). Grand Rapids, MI: Baker Book House.
**Cairns, A. (2002). In Dictionary of Theological Terms (pp. 249–251). Belfast; Greenville, SC: Ambassador Emerald International.