The Kingdom of God
When Jesus began to preach, he said, 'The time has come... The kingdom of God has come near. Repent and believe the good news' ( Mark 1:15 ). The kingdom was a constant theme in many of his parables ( sometimes called 'the kingdom of heaven'). This picks up the Old Testament idea that God is Lord of heaven and earth and that he blesses those who live under his rule.
Jesus taught that his work of healing and delivering people from demonic powers were a sign 'the kingdom of God has come upon you' ( Matthew 12:28 ). He also taught that he must suffer things, be killed, and on the third day be raised to life. The perfect and full experience of the kingdom of God would come with his return. That's why, in the Lords Prayer, Jesus encourages us to pray 'your kingdom come'.
When you see Christians loving and serving each other you can see the Kingdom of God at work. Wherever you see people resisting sin and temptation, you see the kingdom of God at work. But what we experience now is only a forestate of what is to come, when we will live with Jesus forever.