In his Avodas Ha’Gershuni, commentary to Shir HaShirim, the nephew of the Gaon, zl, m’Vilna (son of Horav Avraham, the Gaon’s brother) writes that he heard from his revered uncle a reason why Succos is celebrated during the month of Tishrei (fifteenth), rather than Nissan which coincides with the liberation from Egypt. The Torah (Vayikra 23:43) indicates that the Succos festival was initiated because, “I caused Bnei Yisrael to dwell in succos/huts when I took them out of the land of Egypt.” If so, why is Succos not celebrated in Nissan?
The Gaon explains that the underlying reason for Succos is Hashem’s acquiescence to return the Divine Presence to Klal Yisrael via the Mishkan. The commencement of this return occurred on the fifteenth of Tishrei. Moshe Rabbeinu descended from Har Sinai on Yom Kippur, the tenth of Tishrei. He then announced that the people were to build a Mishkan for Hashem’s return. On the twelfth and thirteenth (ba’boker ba’boker, morning after morning), they brought their contributions. On the fourteenth, Moshe declared an end to the contributing phase; they had sufficient contributions. On the fifteenth day, when we begin Succos, the Jews began the work of building the Mishkan and its vessels. This is when we merited to reside beneath the kanfei, wings, of the Shechinah. This was the return of the Ananei ha’Kavod, Pillars of Cloud. On the fifteenth of Tishrei, Hashem’s return indicated His forgiveness for the sin of the Golden Calf. Thus, we celebrate Succos in Tishrei.
