It is a kingdom which is to come, yes.  But it is also a kingdom which has come. “The kingdom of God is among you” and “within you.”  The kingdom of God is in every true Christian.  He reigns in the Church when she acknowledges Him truly.  The kingdom has come, the kingdom is coming, the kingdom is yet to come.  Now we must always bear that in mind.  Whenever Christ is enthroned as King, the kingdom of God is come, so that, while we cannot say that He is ruling over all in the world at the present time, He is certainly ruling in that way in the hearts and lives of all His people