Luke 17:20-21 (NKJV)
Now when He was asked by the Pharisees when the kingdom of God would come, He answered them and said, "The kingdom of God does not come with observation; nor will they say, 'See here!' or 'See there!' For indeed, the kingdom of God is within you."
The Jews were expecting a messiah who would restore their great kingdom, an earthly reign. Jesus makes it clear here that the kingdom of God is a relationship. We learn in school that a kingdom has boundaries geographically. But a kingdom also has a King and his subjects. When a person makes Jesus Lord, he is granting Jesus authority to rule and reign in his life. That is a kingdom relationship.