If you have not already done so, I encourage you to read the Prologue to this study, as it provides the framework for understanding the rest of it. Remember that Revelation consists of seven visions which state the same theme of Jesus as Lord.
Seventh Vision: New Heaven and Earth (Revelation 21-22:5)
John had a few previews of this vision, such as when the sixth seal was broken, but this vision is in High-Definition broadcast. Every vision, image, and declaration starting from where Jesus stood among the lampstands lead to this point. The old is judged and discarded so that the new can be ushered in. God would no longer inhabit Heaven alone, but directly inhabit His people. The old heaven and earth will be a distant memory, for the new heaven and earth will be joined as one even as Jesus and the Bride will be united as one. God will dwell among us, and we will live with Him—no separation, no boundary, no distance.
The New Jerusalem is contrasted with two things:
Firstly, it is contrasted with the physical city of Jerusalem. Let us remember the “old Jerusalem” was destroyed in A.D. 70 by the Romans, fulfilling Jesus’ prophecy that “one stone would not be left on another.” Early Christians would’ve been waiting for that prophecy to be fulfilled in their lifetimes. This symbol would be a great comfort to those who saw the city of Jerusalem fall, reminding them that everything which made Jerusalem special now applied to them (and, by extension, us) as the people of God.
Secondly, the New Jerusalem is contrasted with the fallen city of Babylon in previous visions. Both are compared to women; Babylon a whore and Jerusalem a bride. The New Jerusalem is referred to with personal pronouns (“her”) until the city comparison takes full form. Therefore, it is not just a depiction of a celestial city, but a visual expression of the glory of the age-to-come invested within the pure and spotless Bride united with her Groom.
The abode of God among men will be man himself, and the division between flesh and spirit will be gone. Much emphasis is given to the streams of living water from the throne which give life, and to the tree of life which heals all wounds. Many of these images and ideas come directly from Old Testament prophecy and even descriptions of the Garden of Eden itself. The saints will be truly made like Jesus as He makes all things new.
Much more could be said of this vision, as with the others, but the words of John provide a plain meaning that makes further exposition unnecessary.
Epilogue (Revelation 22:6-21)
As the visions begin to fade and John begins to reflect upon all he has seen, he becomes adamant on several points:
While there is certainly much to be gleaned from finer examination of the preceding passages, I feel that this has been an accurate presentation of the core message and central theme of “the revelation of Jesus Christ and of what must shortly come to pass.”