Tetzaveh: Chapter 15
Four kinds

Rabbi Shimon and the old sage discuss the verse, "And you shall take for yourselves on the first day the fruit of the tree hadar," saying that "hadar" is the Righteous, namely Yesod, and that Malchut is the "fruit of the tree hadar." They speak about the palm trees, the boughs of thick leaved trees, and the two willows of the brook. They conclude that we are commanded to take these four kinds since we need to awaken below in the likeness of above. There is nothing in the world that has no counterpart above, and the reverse is also true.