God's kingdom (the Kingdom of Heaven in Matthew's gospel) is a widely misunderstood concept in our day. The most common misconception is the identification of the Kingdom of God with the Church. Neither the first Christians nor the Jews understood it like that. And Jesus never encouraged that idea.
It is instructive to start by looking at the instances when Jesus was talking about it. He started his Galilean ministry "preaching the good news of the Kingdom of God, saying, the time is fulfilled, and the Kingdom of God is at hand" (Mark 1:14-15). The Kingdom was present because its king was present. The time was fulfilled because Jesus had recently been baptised, and the Holy Spirit had descended on him to anoint him for his task of spreading the good news (gospel).
The Jews had reasonable consensus on what the Kingdom of God was to be like. From many passages in the Old testament they concluded that a king, not too different from David, would inaugurate a time of peace and prosperity for Israel which would impact the whole world. "The word of the Lord would be proclaimed from Jerusalem" (Isaiah 2:3). Jesus did not at any time contradict this notion. The teachers of the Jewish Bible taught that the Messiah would be known as the "son of David" (Mark 12:35) and that title was given to Jesus by those who believed in him (Matthew 9:27; 12:23;15:22; 20:30; 21:9,15).
In Bob Mumford's exposition of the Sermon on the Mount, he called that sermon the constitution and bylaws of the Kingdom of God. Jesus told many parables to explain aspects of the Kingdom of God but only on two occasions did he mention the church (Matthew 16:18; 18:17). He taught us to pray that the Father's kingdom would come. A week before going up onto the Mount of Transfiguration Jesus said that some of the disciples would not taste of death before they had seen the Kingdom of God come with power (Mark 9:1).
The antagonistic Pharisees asked Jesus when the Kingdom of God would come. Jesus never encouraged morbid curiosity about future events and certainly would not entertain his enemies with his knowledge of the future just to tickle their ears. In essence he told them the Kingdom of God had already come but they did not recognise it (Luke 17:20-21). To his disciples he explained what he meant by "in your midst". The King was in their midst right then, he would be gone for a long time, and would come again for every eye to see him (Luke 17:22-24; Revelation 1:7).
Every opportunity Jesus used to let the apostles understand he had to die and rise again they misunderstood. They thought he meant the Kingdom of God would be coming to earth right then. They were all bashful when he told them not to be jockeying for position in the Kingdom, maybe because it showed up their complete insensitivity to the ordeal he had to face (Mark 9:31-35). Just before they reached Jerusalem he spoke about his passion again. This time James and John decided to use the occasion to ask for the best posts in the Kingdom (Mark 10:33-37). Even on the Last Supper they were still arguing about their positions in the coming kingdom (Luke 22:24).
When the multitude following Jesus approached Jerusalem on Palm Sunday they thought the Kingdom of God was "about to appear"(Luke 19:11). The crowd would have crowned him king there and then. The Pharisees knew that (John 12:19).
Finally, when Jesus was ready to ascend into heaven, the apostles still did not get it (Acts 1:3-7). It is important to notice that Jesus did not "correct" them by telling them that their concept of God's kingdom is all wrong. The kingdom will be restored to Israel as many present day Jews believe. Christians who trust the reliability of the Old Testament believe so too. Messianic Jews believe it will happen when the rulers in Jerusalem say: "Baruch Haba B Shem Adonai", Hebrew for "Blessed is he who comes in the name of the Lord" (Matthew 23:37-39).
But first they will accept as a ruler "one who comes in his own name" (John 5:43). That is the one who will declare himself a god (2 Thessalonians 2:4). But when Jesus appears he will get rid of the antichrist "by the breath of his mouth" (2 Thessalonians 2:8).
