Luke 17.20-24
20 Being asked by the Pharisees when the kingdom of God would come, he answered them, “The kingdom of God is not coming in ways that can be observed, 21 nor will they say, ‘Look, here it is!’ or ‘There!’ for behold, the kingdom of God is in the midst of you.” 22 And he said to the disciples, “The days are coming when you will desire to see one of the days of the Son of Man, and you will not see it. 23 And they will say to you, ‘Look, there!’ or ‘Look, here!’ Do not go out or follow them. 24 For as the lightning flashes and lights up the sky from one side to the other, so will the Son of Man be in his day.
Some interpreters think this text shows that the kingdom has nothing to do with the future renewal of the earth, but rather that it is merely recognizing God’s reign in your heart. The following remarks from Albert Nolan help explain this misunderstanding:
Many Christians have been misled for centuries about the nature of God’s kingdom by the well-known mistranslation of Lk 17:21: “The kingdom of God is within you.” Today all serious scholars and translators agree that the text should be read: “The kingdom of God is among you or in your midst.” The Greek word entos can mean “within” or “among” but in the present context to translate it “within” would mean that in answer to the Pharisees’ question about when the kingdom of God would come (17:20) Jesus told them that the kingdom of God was within them! This would contradict everything else Jesus ever said about the kingdom or about the Pharisees. Moreover, since every other reference to the kingdom presupposes that it is yet to come and since the verb in every other clause in this passage (17:20-37) is in the future tense, this verse must be understood to mean that one day they will find that the kingdom of God is suddenly and unexpectedly in their midst.
The kingdom of God, like any other kingdom, cannot be within a person; it is something in which a person can live. Somewhere in the background behind Jesus’ use of the term “kingdom of God” there is a pictorial image. He speaks of people entering into the kingdom (Mk 9:47; 10:15, 23, 24, 25, parr; Mt 5:20; 7:21; 18:3; 21:31; 23:13; Jn 3:5). They can sit down in it and eat and drink in it (Mk 14:25; Mt 8:11-12 par; Lk 22:30). The kingdom has a door or a gate (Mt 7:13, 14; Lk 13:24) on which one can knock (Mt 7:7-8 par; 25:10-12 par). It also has keys (Mt 16:19; Lk 11:52) and can be locked (Mt 23:13; Lk 13:25). The pictorial image behind this is obviously that of a house or a walled city.
…The fact that his way of speaking about the kingdom is based upon a pictorial image of a house, a city or a community leaves no doubt about what he had in mind: a politically structured society of people here on earth. A kingdom is a thoroughly political notion. It is a society in which the political structure is monarchical, that is to say, it is ruled and governed by a king. Nothing that Jesus ever said would lead one to think that he might have used this term in a non-political sense.
(Albert Nolan, Jesus Before Christianity, (Maryknoll, NY: Orbis Books, 1992) pp. 58-59.)
Another idea is that as the Messiah, Jesus represented the kingdom wherever he went. We might even imagine a kingdom bubble around Jesus. When he was present the kingdom was present. Thus, the kingdom was looking the Pharisees right in the face and they did not perceive it.

The above was taken from:Is the Kingdom within You?