"On the fifteenth day of the seventh month, when you have gathered in the produce of the land, you shall celebrate the Feast of Tabernacles to the Lord for seven days. Both the first and the eighth day must be a day of absolute rest for you.", Leviticus 23:39.
"During these seven days you shall dwell in booths; this applies to every Israelite born." Leviticus 23:42.
God asks the Jews to make a booth (Sukah) with the Feast of Tabernacles (Sukkot) and to live in it. He does this to make them aware of the fact that there will come a time when all will leave their homes to go with the Messiah and the angels to God and live with God in Heaven where he has prepared for them to stay :
"In my Father's house are many mansions (otherwise I would have told you), for I go to prepare a place for you; and when I go and prepare a place for you, I will come again and will take you, that where I am you also may be.", John14:2-3
GOD YHWH sends Christ and the angels to come and get us to live with HIM in Heaven:
"But don't we believe that Jesus died and rose from the dead? Then it follows that God will bring to Himself those who died as Christians with Jesus.
We keep a word from the Lord when we say to you: We who are still alive until the coming of the Lord have no precedence over those who are dead.
For when the sign is given, the archangel lifts up his voice, and God's trumpet sounds, the Lord himself will come down from heaven. Only then do the dead Christians rise; then we who are still alive will be caught up with the resurrected in the clouds in the air to meet the Lord. Then we will be with the Lord forever." 1 Thessalonians 4:14-17.
So the 7-day Feast of Tabernacles is about this move towards God, to prepare for it.
The 8th day closing this Feast is about the closing of what this Feast stands for, namely the closing of an Earthly life outside God's Presence by sealing God's Spirit to Eternal Life and Will in your life and thus always in God's Presence :
"And on the last, the Great Day of the [Tabernacles] Feast, Jesus stood and cried, saying: If any man thirst, let him come to me and drink!
Whoever believes in me, as the scripture says, rivers of living water will flow from within him.
This spake he of the Spirit, which they that believed in him should receive; for the Spirit was not yet given, because Jesus was not yet glorified." John 7:37-39.
And so the journey and migration of those who belong to God are sealed and they are now literally in God's Presence, but also figuratively always in God's Presence: with a heavenly body with God's Eternal Spirit sealed in it. And that is certainly what Christians celebrate in order to determine what is to come for them as well.
Celebration for Christians
Leviticus 23:42 makes it clear that the Tabernacle habitation applies to "born Israelites" or in Israel. There the provisions of the Tabernacle are no longer kept; they are usually plastic tents - often on a balcony or as an extension in the garden - that are equipped with all modern conveniences (microwave, table, chairs, TV, etc.), but no longer made of flowering wood, etc.
Christians are therefore not obliged to live in a booth, which is very nice given the often cold autumn days. And for those who want it anyway: an awning of a balcony or a tent set up in your garden is sufficient.
More importantly, the first day of Tabernacles and the concluding 8th day are kept as a SABBATH: not working/earning money/trading, but with a focus on rest, being together, having festive meals together, and so on. I usually add the 7th holiday as well.
Life in the new heavenly Jerusalem