Heaven is above. Earth is below. These are two different places.
Jhn 8:23But he continued, "You are from below; I am from above. You are of this world; I am not of this world.
When death is no more at the end of the millenium, because the last enemy destroyed is death, the city of God will come down.
Revelation 21
1And I saw a new heaven and a new earth: for the first heaven and the first earth were passed away; and there was no more sea.
2And I John saw the holy city, new Jerusalem, coming down from God out of heaven, prepared as a bride adorned for her husband.
3And I heard a great voice out of heaven saying, Behold, the tabernacle of God is with men, and he will dwell with them, and they shall be his people, and God himself shall be with them, and be their God. 4And God shall wipe away all tears from their eyes; and there shall be no more death, neither sorrow, nor crying, neither shall there be any more pain: for the former things are passed away.
This is why the people of the earth practice the feast of tabernacles during the millenium - in preparation for what comes at the end of the millenium.
Zech 14: 16And it shall come to pass, that every one that is left of all the nations which came against Jerusalem shall even go up from year to year to worship the King, the LORD of hosts, and to keep the feast of tabernacles.
17And it shall be, that whoso will not come up of all the families of the earth unto Jerusalem to worship the King, the LORD of hosts, even upon them shall be no rain.
18And if the family of Egypt go not up, and come not, that have no rain; there shall be the plague, wherewith the LORD will smite the heathen that come not up to keep the feast of tabernacles.
19This shall be the punishment of Egypt, and the punishment of all nations that come not up to keep the feast of tabernacles.
20In that day shall there be upon the bells of the horses, HOLINESS UNTO THE LORD; and the pots in the LORD's house shall be like the bowls before the altar. 21Yea, every pot in Jerusalem and in Judah shall be holiness unto the LORD of hosts: and all they that sacrifice shall come and take of them, and seethe therein: and in that day there shall be no more the Canaanite in the house of the LORD of hosts.