Question: In Zechariah 14:16-21 it says that when our Lord returns everyone will go up to Jerusalem year after year to celebrate the Feast of Tabernacles. What does that mean. Is He going to re-institute this feast for everyone to keep?
Response: Yes, it is my understanding from the straightforward sense of this passage that Tabernacles will be a festival to which all the worlds' peoples will be required to send representatives. And, I would imagine, that all who consider themselves followers of the Lord will want to assemble before Him in Jerusalem once a year (cf. "three times a year" in ancient Israel: Ex.23:14-17).
The feast of Tabernacles is significant in this regard because it is the festival which looks forward to the Millennial Kingdom of the Messiah (for the Israelites will dwell "in booths" when they re-enter the land, just as that first generation in the promised land had done). Therefore this feast will be a memorial and a celebration of the Messiah's reign (and of Israel's return to the land – God having fulfilled all of His promises to them in this regard). As far as other nations are concerned, failure to come to this festival would naturally constitute a grave offense, for that would be saying, in effect, that they were not happy with the King's rule (cf. Lk.19:14; 19:27). And we know, of course, that in spite of the perfect righteousness of His rule and the glorious conditions of the Millennium, there will, nevertheless, be many who will become bitter and dissatisfied, even to the point of rebelling against Him in the end (cf. Ps.2; Rev.20:7-9).
For more on the symbolism of the Feast of Tabernacles, see part 5 of the Satanic Rebellion series, under "Booths (Tabernacles)", section II.8.c.7.
For the Millennium in general, please see the following links:
The Millennium and New Jerusalem (CT 6)
Animal sacrifice in the millennium.
Does the Bible teach a literal Millennium?
Who will populate earth during the Millennium?
Longevity in the Millennium.
Hope this helps with your question.
Yours in anticipation of His wondrous reign.