The Sukkah & The Ark
The Zohar says that the sukkah is comparable to Noach's ark. Just as Noach's ark protected its occupants from the raging floods, so does the sukkah protect us from all evil. The Gemara says that only those who had not sinned were admitted into the ark. Perhaps this is why Sukkos falls right after Yom Kippur. Since on Yom Kippur Hashem has forgiven all our sins, we deserve to dwell under the protective shield of the sukkah.