The Mishnah states that if one makes his Sukkah among the trees and the trees serve as walls for the Sukkah, the Sukkah is valid.
This statement can be interpreted homiletically to mean that a Sukkah, which symbolizes man’s frailty, should be built amongst the trees, i.e. the righteous, who are likened in Scripture to trees. When the spies returned from Eretz Yisroel with their disparaging report, Calev responded to them, “their protection has departed from them; HaShem is with us. Do not fear them.
The Medrash states that the protection of the Canaanites was Iyov, a righteous person, who had died. Thus, we see that the righteous are referred to as the protectors, and the righteous protect the nation just like a Sukkah provides shade for one dwelling inside. When one dwells in the Sukkah, he is not alone, because the Ushpizin, the seven righteous Patriarchs and leaders of the past, are also with him in the Sukkah.