The children of Israel left Egypt in the Hebrew month of Nisan, in springtime, and immediately the sukkot — the booths of the wilderness — went up. They lived in these booths for forty years. If the memory is to be commemorated honestly, the rabbis asked, why not commemorate it in the season it actually happened? Why did God command us to dwell in booths in autumn, in the month of Tishrei (see Leviticus 23:34, 42-43)?
After all, the Israelites lived in booths through every season of the year — spring, summer, fall, and winter. Any of the four would serve as a reminder.
The midrash on Sukkot gives a simple, devastating answer.
If we dwelt in booths in the summer, no one would know why we were doing it. Half the neighbors would assume we were simply escaping the heat — taking shade under palm fronds as any sensible person does. The commandment would disappear inside the convenience.
But in the fall, when the trees begin to drop their leaves, and the wind grows cold, and the rain begins to chill the bones, and every practical instinct is telling us to seal our windows and repair our solid houses for winter — that is when we leave our warm homes and step out into a booth of branches. No one could mistake it then for a comfort-seeking choice. The inconvenience itself declares the intention: we are doing this because God asked us to.
The autumn rain is part of the mitzvah. It proves that the sukkah is not a vacation. It is an obedience.