Chapter 23 of the Book of Leviticus outlines two mitzvot associated with the festival of Sukkoth. In verse 40 it says
“On the first day [of the festival] you shall take the product of hadar trees, branches of palm trees, boughs of leafy trees and willows of the brook…..”.
These are the four species of vegetation that we today know as the etrog, lulav, myrtle and willow. The Rabbis taught that we hold the four species together, and wave them in all of the directions of the compass, as well as upwards and downwards. In this way, we mobilize the winds that blow from all directions to bring rain to Israel for the new season of sowing and harvest.
In Leviticus 23: 42-43 we read,
“He shall live in booths [Sukkoth] seven days; all citizens in Israel shall live in booths, in order that future generations may know that I made the Israelite people live in booths when I brought them out of the land of Egypt…..”.