“The festival of Sukkot does not commemorate any specific event, but is a reminder, as it says in the Torah, ‘that your generations may know that I made the children of Israel dwell in booths, when I brought them out of the land of Egypt.’ (Lev.23:43).
Our sages differ about whether this refers to the protective Clouds of Glory that covered the Israelites in the desert or to the actual exodus from Egypt and their wanderings in the wilderness, protected by God against all harm.
In any case, according to the deeper interpretation of this question, the festival of Sukkot is not merely a reminder of the past.
Sitting in the Sukkah serves to emphasize, once again, that we are protected under the shelter of God’s wings.”
–Rabbi Adin Steinsaltz
From A Guide to Jewish Prayer, p. 169, by Rabbi Adin Steinsaltz