This is true only until the Second Coming of Christ. After that the Kingdom of God will be evident on earth as a real, physical, worldwide Kingdom with redeemed nations on earth and Christ as King.
And the seventh angel sounded; and there were great voices in heaven, saying, The kingdoms of this world are become the kingdoms of our Lord, and of his Christ; and he shall reign for ever and ever. (Rev 11:15).
Once again, this reminds us that unless Christians take ALL Scriptures into account, they will not understand God's plans and purposes.