World history has witnessed a multitude of divergent forms of government. The most common types have been dictatorships ruled by military strength, republics ruled by law, democracies ruled by majority vote, and two types of monarchies—constitutional monarchies (in which the monarch's powers are limited) and absolute monarchies (in which the monarch's word is law).
The kingdom of God is an absolute monarchy. God has no external constitution to bind Him. He needs no consent from the governed to rule over them. He is not limited by referenda or by majority vote. His word is law; His rule is absolutely sovereign.
In any monarchy, the virtues of honor and loyalty to the throne are exceedingly important. There is no monarchy where these elements are more vital than in God's kingdom. Yet the fundamental sin of the human race is grounded in our refusal to honor God as God (Romans 1:21) and in our disloyalty to the King of Kings.
The theme of the kingdom of God is a central motif that runs as a thread through both Old and New Testaments. The theme accents God's reign over His people. The coming Messiah is announced as God's anointed King who will be enthroned in heaven as the King of Kings and Lord of Lords.
The Old Testament points to the kingdom as coming in the future. The New Testament opens with the announcement of John the Baptist that "the kingdom of heaven is at hand" (Matthew 3:2). The historical situation is described in images such as "the ax is laid to the root of the trees" (Matthew 3:10) and "His winnowing fan is in His hand" (Matthew 3:12), both indicating radical nearness. It was the breakthrough into history of God's kingdom that heralded the New Testament gospel. John's message that "the King is coming" signaled the urgency of the times.
The accent of Jesus' own preaching also falls on the announcement of the gospel of the kingdom. He declares that the kingdom has come with power and is in the midst of His people. At His ascension, Jesus commanded His disciples to be His witnesses in the world. They are to witness to the reign of Jesus as King of Kings. Jesus' current status as cosmic King is invisible. The world is either ignorant of His sovereignty or denies it. It is the task of the church to give visible witness to the invisible kingdom.
Jesus inaugurated the kingdom of God. He has already been enthroned in heaven. But it is as though He is a King in exile with few loyal subjects. At His return He will fully consummate His reign.
The New Testament indicates that the kingdom of God is both present and future. There is an "already" and a "not yet" to the kingdom. Both aspects must be understood and embraced by Christians. To view the kingdom either as already totally realized or as totally futuristic is to do violence to the message of the New Testament. We serve a King who has already been enthroned. Yet we await His triumphal return in glory when every knee will bow before Him.