The Men of the Great Assembly established Sukkot as “the time of our rejoicing,” and one should rejoice on it in an extra measure, more than on the other holidays. For although the others are indeed all “holidays for rejoicing,” only Sukkot is defined as “the time of our rejoicing.”

The reason is perhaps as follows: On Pesach and Shavuot the Jews are on the level of tzaddikim. For Pesach was a preparation for the giving of the Torah on Shavuot, and at Sinai the Jews were like converts and therefore considered new-born children, utterly without stain or blemish. However, on Sukkot, which follows the repentance and atonement of Yom Kippur, they are on the level of ba’alei teshuvah.

Therefore there is an extra rejoicing on Sukkot, for the rejoicing of a ba’al teshuvah is superior to that of a tzaddik. The rejoicing of a tzaddik is compared to that of a son who was never separated from his father; however, the rejoicing of a ba’al teshuvah is like the powerful rejoicing of a son who was separated from his father by a great distance and afterwards returned, one distant who became close.

(Sichat Simchat Beit Hasho’eivah 5720)