That's just
inside the new Jerusalem. God will be dwelling there so His glory will light everything. Out side the city it will be similar to now. Notice the tree of life gives its fruit every month, showing seasons and time will continue-just like God said it would forever. The creation and time are tied together. Only God had no beginning. Time is needed to administrate the creation for created beings.
Ezek. 40-48, shows the Temple will last forever too, along with Israel. So, the Heavenly city has no Temple, but this Temple is outside the new Jerusalem, therefore they can both last forever.
No sea, could mean none like we know today-maybe not a blue planet no more? More landmass for people will be a good thing. No reason there cannot be large lakes, or maybe he was talking about the area around Jerusalem? The land will be changed their for sure. Lifted up and there will be a big flat area with a high mountain at one end (the heavenly city). The whole lifted area will be called Zion with both the Temple and the New Jerusalem on the same plateau. It will be a shining city of light!
22But you have come to Mount Zion
and to the city of the living God, the heavenly Jerusalem, and to myriads of angels,
1The word which Isaiah the son of Amoz saw concerning Judah and
Jerusalem.
2Now it will come about that
In the last days
The mountain of the house of the LORD
Will be established as the chief of the mountains,
And will be raised above the hills;
And all the nations will stream to it.
3And many peoples will come and say,
“
Come, let us go up to the mountain of the LORD,
To the house of the God of Jacob;
That He may teach us concerning His ways
And that we may walk in His paths.”
F
or the law will go forth from Zion
And the word of the LORD from Jerusalem.
4And He will judge between the nations,
And will render decisions for many peoples;
And they will hammer their swords into plowshares and their spears into pruning hooks.
Nation will not lift up sword against nation,
And never again will they learn war.
5Come, house of Jacob, and l
et us walk in the light of the LORD.
1In the twenty-fifth year of our exile, at the beginning of the year, on the tenth of the month, in the fourteenth year after the city was taken, on that same day the hand of the LORD was upon me and He brought me there.
2In the visions of God He brought me into the
land of Israel and set me on a very high mountain, and on it to the south there was a structure like a city.
10And he carried me away in the Spirit to a
great and high mountain, and showed me the holy city, Jerusalem, coming down out of heaven from God,
You ought to read "Heaven" by Randy Alcorn. It changed my viewpoint on what Heaven will be like, and got me to dig in about this subject. I believe it will also set down at the start of the 1000 year reign (Rev 21-22 being a parenthetical showing the start of the MK and focusing in on the heavenly city), and be smaller than we think because of cubed measurements. Janet Willis, in he book What on Earth is Heaven like?, has some good ideas about the size and shape of the city. She gave me the last piece of the puzzle.
https://www.amazon.com/What-Earth-Heaven-Like-Jerusalem/dp/1516815130
https://www.amazon.com/Heaven-Randy-Alcorn/dp/0842379428