What shade is needed?
Rashi: It is to protect from the flame of the day to come - "v'Lihat Osam ha'Yom ha'Ba" (Mal'achi 3:19). Hashem will remove the sun from its case, and make it beat on them.
Radak: It is lest the sun, dry heat or rain harm them.
Malbim: It is from constant evils, like dry heat, and from those that come occasionally, like Zerem and rain. Hashgachas Hashem protects from opposites. The verse depicts that the evil itself will protect the Tzadikim - the Sukah will be "me'Chorev
Whom will the Sukah cover?
Radak citing Targum Yonasan: It will cover Yerushalayim.
What is "Machseh"?
Rashi: It is a cover.
Malbim: It is a small protection.
What is "l'Mistor"?
Rashi: It is to hide in it.
Malbim: It is a great protection.
What is "mi'Zerem"?
Rashi (from Chagigah 13a): It is a shower of fire from the Dinor river, on Resha'im in Gehinom - "Al Rosh Resha'im Yachul" (Yirmeyah 23:19).
Malbim: It is a great downpour of rain.
What rain is discussed?
Rashi: It is rain that descends on Resha'im - "Yamter Al Resha'im Pachim" (Tehilim 11:6).
Malbim: It is normal rainfall. They will be saved even from minor mishaps.
