In Luke 17:20–21, Jesus says, “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 context of Jesus’ statement is a question put to Him by His Pharisee detractors who had asked when the kingdom of God would come.
Jesus’ answer was that the kingdom of God was not coming in the manner the Pharisees (or we still today) were expecting. The kingdom would not be inaugurated with spectacle or splendor; there would be no great and magnificent leader who staked out a geographical claim and routed the Romans; rather, the kingdom would come silently and unseen, much as leaven works in a batch of dough (see Matthew 13:33).
In fact, Jesus says, the kingdom had already begun, right under the Pharisees’ noses. God was ruling in the hearts of some people, and the King Himself (Jesus) was standing among them, although the Pharisees were oblivious to that fact.