After the first heaven (our present universe) and the first earth (our present earth) are passed away (destroyed), God will give us a new heaven and a new earth.

Revelation 21:1-2

Then I saw a new heaven and a new earth; for the first heaven and the first earth passed away, and there is no longer any sea. 2 And I saw the holy city, new Jerusalem, coming down out of heaven from God, made ready as a bride adorned for her husband.

And the new heaven and earth will be somewhat blended together as one. This process of blending is when the third heaven (God’s eternal dwelling) is expanded to encompass our new universe and new earth.

Now as I understand it, the entire process of expansion will be accomplished when the heavenly city descends out of the third heaven to earth. Here is the process in four points.

1. The heavenly city, called the New Jerusalem, will be created by God somewhere in the third heaven. Remember, in verse 2, John saw the holy city coming down out of heaven from God. And it was made ready; that is, it was all finished (in its creation). So. its creation was in the third heaven. And Jesus Himself is the builder (Jn. 14:2).

2. This holy city (described in Rev. 21:9-21) will descend from heaven after the New heaven and earth are created. And I think it will either hang over the earth or sit on the earth. And so, the third heaven will be extended down by the holy city to the new earth. Hence the city will be as a gateway or a bridge linking the eternal heaven to the new earth.

3. This New Jerusalem, we think, will be the capitol city of heaven, and it will be where the throne of God is and where the focus of all of heaven is.

4. This city, as we have mentioned, is where we as believers will dwell. We will have our own room that He has made for us (Jn. 14:2). But that doesn’t mean that we are stuck there; for the gates of the city will never be closed (Rev. 21:25). I imagine we will be able to go anywhere we desire in the city, on the new earth, or anywhere in the new heaven—which will then be the new and eternal universe that will have no boundaries and no dimensions. Whereas, our universe now is finite and limited, the new heaven will actually be an extension of the third heaven. So, when John sees the new heaven (in Rev. 21:1) he is actually seeing a new universe that is blended with the third heaven. This is awesome to me and a little scary. But once we get our new bodies and our new mind I imagine that it will be quite exciting and glorious.