The Kingdom of God and the Already - Not-Yet Tension

In thinking about the Kingdom of God, there is an apparent and necessary tension between the Kingdom having come with the incarnation of Jesus Christ, and the Kingdom to come when He returns.  Below is a series of verses that show the tension.  Afterwards is a very brief discussion of why this tension must be maintained.

The Kingdom has already come:
Luke 17:20-21: “Once, on being asked by the Pharisees when the kingdom of God would come, Jesus replied, ‘The coming of the kingdom of God is not something that can be observed, nor will people say, “Here it is,” or “There it is,” because the kingdom of God is in your midst.’”
So, when Jesus came to the earth, it was right for Him to tell others wherever He is, the Kingdom of God is.

The Kingdom is yet to come:
Luke 21:25-31: “There will be signs in the sun, moon and stars.  On the earth, nations will be in anguish and perplexity...Even so, when you see these things happening, you know that the kingdom of God is near.”
However, until Jesus returns a second time, the kingdom of God has not yet come in its fullness.  Thus, it is right for Jesus to say that even as the signs of the end times begin to unfold, the Kingdom of God has not yet come,  but is near.