If the Kingdom of God is perpetually coming, it is never here; it is never now.  No matter how we perceive Jesus, or interpret His teachings, it is hard to refute that reaching the Kingdom of God requires a shift in consciousness and demands arrival at a higher level of awareness.

If the Kingdom of God is within, then it is not physical but spiritual.  The Kingdom of God is realized in the awakening of consciousness, not in the awaiting of a physical return.  Many have been anticipating the physical while negating the spiritual.  How many dates have been set and reset as the appointed time for Christ to physically return to the earth?  How many times can we predict and then re-predict this long awaited event?  Christianity has been "stood up" for two thousand years, waiting on a date that has yet to arrive.
 
It is human nature to try and make the spiritual . . . physical.  If we can touch it or see it, we can sense it and then understand it.  Yet, turning the spiritual into physical is idolatry.  Moses raged against Aaron for creating a physical image of God because the basic principle of Judaism was that God was both abstract and unimaginable.  God transcends physicality to the point that in the Hebrew tradition the sacred name of God (Yaweh) could not be written or spoken.  In other words, it was forbidden to turn the spiritual in to physical.
 
If the Kingdom of God is within, why are we searching for it without?  If the Kingdom of God is a spiritual realm of consciousness, why are we waiting for it physically?  If the Kingdom of God is within, would the Coming Kingdom be anywhere other than within?  Even if Christ returned physically, He would still be endeavoring to set up the Kingdom of God within us!