NOTES for Rev 21:24
The image of the heavenly Jerusalem first appears in the preaching of Isaiah of Babylon, who lived six centuries before Christ's coming. Even then it was like the description we find in the Book of Revelation: a shining city on the top of a mountain, to which earthly kings give glory and which becomes light not only for the people of God, but also for the pagans. The corresponding Greek verse speaks of "nations," that is, pagans, who will walk in "its," the city's, light; the word "saved" is a later insertion absent from early editions of the Book of Revelation.
What is greater here: reality or symbol? The earthly Jerusalem or a heavenly vision? The answer is not as simple as it may appear. Of course, when one reads of the glory of God that replaces both sunlight and moonlight here, only heaven comes to mind, and certainly not our sinful world. Meanwhile, the glory of God, as the biblical books call that radiant presence of God first seen by Moses when he approached the burning bush, accompanied the Jewish people throughout all their history, although before the full transfiguration of the world it could not be revealed to people in the fullness in which Isaiah of Babylon and the apostle John contemplate it.
The difference between earth and heaven in this case is not absolute. God's presence was revealed both before the Messiah's coming and before the full transfiguration of creation, only not in the fullness in which it appears at the end of times. What, then, about Jerusalem? Where is it located: in heaven or on earth? It is impossible to answer this question unequivocally, not because the text is unclear, but because there is no answer.
There would be one if God from the beginning had created heaven and earth as two different worlds with different laws that were not supposed to intersect with each other. However, in the text of the creation poem from the first chapter of Genesis, "heaven and earth," whatever is meant by this, are still one single world, not two different worlds.
A two-world order is not God's design; it is a consequence of the fall, the result of the action in the world of a will opposed to God. This will did not manage to subject the world completely to itself, but it did manage to tear away from it a part that fell under its power.
God, transfiguring the world, frees it from division, so that everything is preserved in it except evil and sin, for which there can be no place in the Kingdom. The Jerusalem we see in the Book of Revelation is heavenly no less than earthly, and earthly no more than heavenly. Only heaven and earth are no longer the same: the transfigured Jerusalem stands on the new earth under the new heaven.