In the Kingdom, Torah will go forth from Jerusalem, and the WHOLE WORLD will keep it. There are three Holy Days that require sojourn to Jerusalem: Passover (Pesach), Pentecost (Shavuot), and Tabernacles (Sukkot)... The prophets proclaim all three... And, btw, the weekly Sabbath (shabbat) on the seventh day too... the end of Ezekiel, Isaiah, and Zechariah would be good for starters....
Correct me if I’m wrong, but there is only one Jewish Holy Day that the non-Jewish nations of the earth will be required to celebrate... and that is Sukkot! Now, there are 3 pilgrim festivals, like you indicated, but in the Millennium it will only be Sukkot. It will be to the point that those nations that don’t celebrate it, won’t get any rain that year. Considering that we are talking about the Millennial Kingdom, that all the prophecies of the Holy Days will be fulfilled... I always thought it was kind of funny the requirement for celebrating Sukkot. I just wonder if Sukkot happens to be the birth date for the King of Kings, it would make sense to celebrate, wouldn’t it?