If Rosh Hashanah and Yom Kippur prepare the mind for teshuvah, repentance, and help the soul achieve divine forgiveness, then Sukkot is like a congratulations party for the body after a long, spiritual journey.
Also called zeman simhateinu, the season of our rejoicing, Sukkot is about joy and giving thanks. When the children of Israel were wandering in the desert after leaving the slavery of Egypt, they had nothing with them except what they could carry. Their sole dependence was on their leaders and on G-d:
G-d brought them manna for food (Exodus 16:4-16) clouds for shelter (exodus 33:14-17; Numbers 9:15-23) water to drink (exodus 15:22-25; 17:5-7; Numbers 20:7-12) and special environmental conditions to prevent their clothing from falling apart (Deuteronomy 29:4). The Sukkot in which they lived provided the protection they needed to feel safe until they reached the land of Israel.
Once they settled the land of Israel, the Jewish people planted and harvested, built houses, dug wells and made their own clothes. The booths they lived in for a week once a year, served as a reminder of how they began. As the Torah warns:
When you later have prosperity, be careful that you not say to yourself, It was my own strength and personal power that brought me all this. You must remember that it is G-d your Lord who gives you the power to become prosperous. (Deuteronomy 8:17-18).
Likewise, living in a sukkah today, even for just one week, teaches us that all we have, the very roof over our heads, is from G-d, and not by our own might.