Why would God demand that people in Millennium should celebrate the Feast of Tabernacle ?
Zech 14:16 Then the survivors from all the nations that have attacked Jerusalem will go up year after year to worship the King, the LORD Almighty, and to celebrate the Festival of Tabernacles.
Because its a commemoration of the time when
God led the Hebrew out of Egypt and they dwelt in tents during their passage through the wilderness to the promised land and they must built a Tabernacle for God to appear as Shekinah Glory to protect them.
Animals offerings was first sacrificed at the Tabernacle of God in the desert in the middle of their booths.
Animals sacrifices in the Tabernacle will be brought back into Millennium as its one set of Hebrew's experience living in the booth at the desert.
So that newly born people in Millennium can begin to appreciate the awesome purpose and meaning of Christ’s Sacrifice and how God looks at sin.
I hope you have caught the picture.