Chapter twenty-one introduces the culmination of all things. After all of the saints have been resurrected and all unbelievers have been banished in punishment, Heaven and Earth will be destroyed and re-created (Revelation 21:1-2). It is in this eternal state that the promise of no tears, sickness, death, etc. will finally be realized (Revelation 21:4). Most importantly, God himself will be with the saints, and we with him, for eternity (Revelation 21:3, 5-8).
Onto this new Earth will come a new Jerusalem, unlike anything this world has seen. The description of the city that John saw is how “heaven” is usually described, but this is not the Heaven that now exists, that believers enter upon death. This city is yet to come. That the city’s foundation and gates are embossed with the names of the twelve tribes of Israel and the twelve apostles shows that there will be some distinction between Israel and the Church for eternity. How far that distinction goes is not revealed, but “the nations” are mentioned in Revelation 21:24-26 and in chapter 22. This is a usual term for non-Jewish people groups.
One significant point regarding the size of the city that John had to measure demonstrates that this is different than the city that Ezekiel measured in chapter 48 of his prophecy. It is clear from the differences that, although Ezekiel did not know it, his prophecy was of the Millennial city and temple, whereas John saw the eternal city. This is also apparent from the fact that John noted that there will be no temple in the eternal city (Revelation 21:22).