SEE - this is where you have believed a lie for Revelation chapter 21 has not been fulfilled = not even close!!!
God and Heavenly Jerusalem will NOT come down to this present Age where satan is still ruling over a world of darkness.
FIRST - the KING of kings must Return and destroy the kings of this earth = Revelation ch19 and Zechariah ch14 and Matthew ch24
Then I saw heaven standing open, and there before me was a white horse. And its rider is called Faithful and True. With righteousness He judges and wages war. He has eyes like blazing fire, and many royal crowns on His head. He has a name written on Him that only He Himself knows. He is dressed in a robe dipped in blood,
c and His name is The Word of God.
The armies of heaven, dressed in fine linen, white and pure, follow Him on white horses. And from His mouth proceeds a sharp sword with which to strike down the nations, and He will rule them with an iron scepter. He treads the winepress of the fury of the wrath of God the Almighty. And He has a name written on His robe and on His thigh:
KING OF KINGS AND LORD OF LORDS.
Defeat of the Beast and False Prophet
Then I saw an angel standing in the sun, and he cried out in a loud voice to all the birds flying overhead, “Come, gather together for the great supper of God, so that you may eat the flesh of kings and commanders and mighty men, of horses and riders, of everyone slave and free, small and great.”
Then I saw the beast and the kings of the earth with their armies assembled to wage war against the One seated on the horse, and against His army. But the beast was captured along with the false prophet, who on its behalf had performed signs deceiving those who had the mark of the beast and worshiped its image. Both the beast and the false prophet were thrown alive into the fiery lake of burning sulfur. And the rest were killed with the sword that proceeded from the mouth of the One seated on the horse.