Sukkot is one of the three Pilgrimage festivals mentioned in the Torah, together with Passover and Shavuot (Pentecost), they were the three times on which people made pilgrimages to Jerusalem to be happy and celebrate.

 

Here are several verses from Leviticus, Verse 23:

 

“Say to the Israelites: ‘On the fifteenth day of the seventh month the Lord’s  Festival of Tabernacles begins, and it lasts for seven days. So beginning with the fifteenth day of the seventh month, after you have gathered the crops of the land, celebrate the festival to the Lord for seven days; the first day is a day of Sabbath rest, and the eighth day also is a day of Sabbath rest. On the first day you are to take branches from luxuriant trees—from palms, willows and other leafy trees—and rejoice before the Lord your God

 

Live in temporary shelters for seven days: All native-born Israelites are to live in such shelters so your descendants will know that I had the Israelites live in temporary shelters when I brought them out of Egypt”.

 

We can see that the Torah gives two reasons for the celebration, the first is agricultural and the second national. Both of them are ways to celebrate the Lord’s work at the change of the seasons, from summer to winter.