For three years Jesus had preached that the kingdom was at hand.  However, after three years of preaching, the kingdom had not come.  When the Pharisees attacked Jesus and demanded to know when it would come Jesus told them where and  how it would come.

And when he was demanded of the Pharisees, when the kingdom of God should come, he answered them and said, The kingdom of God cometh not with observation:  Neither shall they say, Lo here! or, lo there! for, behold, the kingdom of God is within you (Luke 17:20-21).

The kingdom of God was nothing like what the Pharisees imagined.  They were looking for a world ruling physical kingdom like the nation of Rome which would fight and conquer Rome and rule the world.  Jesus said his kingdom was not of this world.  There are only two worlds–God’s and man’s.  If Jesus’ kingdom is not of this physical material world, it must be of the eternal spirit world.  His servants were not called to fight a physical battle, but a spiritual battle against Satan and all spiritual wickedness (Eph. 6:12).  Paul was fighting the same spiritual battle.  He said “For though we walk in the flesh, we do not war after the flesh: (for the weapons of our warfare are not carnal, but mighty through God to the pulling dowan of strong holds” (2 Cor. 10:3-4).  The kingdom of God is not something that could be seen (observed) with physical eyes.  Jesus said “…The kingdom of God cometh not with observation:  Neither shall they say, Lo here! or, lo there! for, behold, the kingdom of God is within you” (Luke 17:20-21). By this we understand the kingdom of God can not be a physical kingdom.  It is eternal and thus can not be physical, for “. . . the things which are seen are temporal; but the things which are not seen are eternal” (2 Cor. 4:18).  Daniel foretold there would be no end to the kingdom God would set up during the Roman rule.

And in the days of these kings shall the God of heaven set up a kingdom, which shall never be destroyed: and the kingdom shall not be left to other people, but it shall break in pieces and consume all these kingdoms, and it shall stand for ever  (Dan. 2:44).

God informs us the earth itself is not eternal (2 Pet. 3:7, 10-13). The angel Gabriel predicted there would be no end to Jesus kingdom (Luke 1:30-33).  His kingdom must be an unseen spiritual kingdom for no physical kingdom can be eternal (2 Cor. 4:18).

Physical kingdoms are made up of physical bodies, physical laws and physical places which will be destroyed.  God’s eternal kingdom is made up of souls, spiritual laws and spiritual places which will never be destroyed.  The stone was cut out of the mountain without hands (Dan. 2:34).  God, not man, set up this kingdom.  God’s kingdom “shall never be destroyed . . . but it shall stand for ever” (Dan. 2:44).