New Jerusalem - the Bride of Christ, Great and Holy City - Revelation 21

In Rev 21, the Bible teaches that a New Jerusalem exists in eternity. But, what does this mean? And, why is it a New Jerusalem. New Jerusalem is the dwelling place of God and His people. It is the Bride of Christ. And, it is also called a holy and great city.

And I John saw the holy city, new Jerusalem, coming down from God out of heaven, prepared as a bride adorned for her husband. And I heard a great voice out of heaven saying, Behold, the tabernacle of God is with men, and he will dwell with them, and they shall be his people, and God himself shall be with them, and be their God. (Rev 21:2-3)

And there came unto me one of the seven angels which had the seven vials full of the seven last plagues, and talked with me, saying, Come hither, I will shew thee the bride, the Lamb's wife. And he carried me away in the spirit to a great and high mountain, and shewed me that great city, the holy Jerusalem, descending out of heaven from God (Rev 21:9-10)