the city of the living God, the heavenly Jerusalem.”
All the prophets pointed to Jerusalem as the place where the Messiah would rule and reign. On the surface this seems self-evident. The trouble with this is that the nature of the Kingdom is spiritual, and so the location of the Kingdom is likewise spiritual. A spiritual kingdom is not going to have an earthly capital. Neither will it have an earthly temple, an earthly priesthood, or an earthly King. It will be in the earth, but it will not rise up from the earth.
Earthly problems cannot be solved with earthly solutions. Earthly problems require Heavenly solutions. The fact that John saw the New Jerusalem coming down out of Heaven and settling upon the earth shows that this is something established by God Himself, quite beyond the command and control of man.