Sukkot: A Pilgrimage Festival

In ancient times, it was customary for Jewish families to travel to Jerusalem to make offerings in
the Temple to celebrate the Shalosh R’galim, or three pilgrimage festivals—Sukkot, Pesach and Shavuot. Sukkot not only celebrates the fall harvest but also calls to memory the booths in which the Israelites slept as they wandered in the desert during the Exodus from Egypt. In Israel, Sukkot marks the beginning of the rainy season, which lasts until Pesach. For this reason, we incorporate a phrase into the weekday Amidah that praises God for rain. In Israel and as part of the Reform Movement, the holiday of Simchat Torah (“rejoicing with the Torah”) is celebrated on the eighth day after Sukkot begins and serves as a post-biblical festival created to honor the Torah.

From The Jewish Parent Page of the Union for Reform Judaism