Matthew 4.17 From that time, Jesus began to preach, and to say, “Repent! For the Kingdom of Heaven is at hand.”
This is one of the most fundamental messages that Christ brought to the world. Jesus appeared during a time of Roman occupation in Israel, a time that many felt oppressed and abused by the system of rule that was in place. There had been a time in Israel's history, when King David and King Solomon ruled, when Israel had been a sovereign nation, not controlled by any foreign power. But those days were long gone. Now Jesus brings a message that there is a greater power, a greater rule in operation, a greater kingdom operating in the present time, that being the Kingdom of Heaven.
In light of this truth, that God himself is the ultimate dispenser of justice and the ultimate sovereign determining the fate of each individual and of whole nations, we should turn away from unrighteous behavior, and seek to serve the Kingdom of Heaven, living under the laws of God's kingdom, without unholy fear of any earthly kingdom.