What is God’s Kingdom?
In general usage the word kingdom means a territory, state or people under the reign of a king or queen. The Bible uses the word kingdom to mean also royal rulership and the authority to reign as king, and in the language of theology God's kingdom is usually understood as indicating his eternal sovereignty. When Pontius Pilate asked Jesus "Are you a king?” he answered, "My kingdom does not belong to this world", indicating that though he had the authority, he was not at that time exercising it (John 18:33-37).
Early in Israel's history God promised to make that nation a kingdom of priests, if they would faithfully keep his laws (Exodus 19:6). They failed to do so and the privilege of becoming these priestly kings was given instead to spiritual Israel (Matthew 21:43), the faithful of the Christian church: "He has . . . made us a kingdom of priests" (Revelation 1:6). The expressions kingdom of God and kingdom of heaven mean primarily the royal rulers who will represent God, exercising authority as his representatives in the next age; in other words, Jesus and the true church – his body members – Will reign over the earth. In poetic language they are said to receive crowns, symbolizing their royal status (1 Corinthians 9:25).
When Jesus commissioned the Apostles to preach, "The kingdom of heaven is at hand", he did not mean that he and the church were about to reign over the earth. Twenty centuries have passed, and we still do not see this accomplished. His thought was surely that the embryo kingdom was about to step onto the stage of human history, to undergo preparation as rulers in the next Age. A change of dispensation had come; instead of preaching Moses and the prophets, God's faithful people were henceforth to preach the Gospel of the Kingdom, and gather first from Israel and then from every nation disciples who would have the opportunity to lay down their lives in service and sacrifice. In this life they suffered as Jesus suffered. In their resurrection, they share his throne.
God's Kingdom is also understood to mean that period frequently referred to in scripture, e.g., as "that day", "the last days", "times of refreshing", "restitution", and “the day of God". The Bible millennium is the thousand years during which Christ reigns over the earth to remove the malign effects of sin.