Question: What do the “four species” of Sukkot (Arba’at HaMinim) mean?
Answer: The four symbols of the celebration of Sukkot are: 1. Lulav (one closed frond from a date palm tree, Yesod), 2. Hadassim (three boughs with leaves from the myrtle tree, HGT), 3. Aravot (two branches with leaves from the willow tree, NHY), 4. Etrog (a fruit from a citron tree, similar to a lemon or grapefruit, Malchut).
All corrections of the souls that are uniting in Malchut of the World of Atzilut (Shechina) occur under the Light of correction that descends from Zeir Anpin (ZA) into her since he is a higher Partzuf (system) in relation to Malchut.
Zeir Anpin, in order to correct the souls in Malchut, groups in three lines, unifying their Sefirot Hesed-Gevurah-Tifferet, and sends the Light of correction from them into Malchut, the souls. In order to evoke such an act from ZA to Malchut, we, the souls who are willing to be corrected (to unite in Malchut), rouse in her its collective desire for correction. Malchut passes this desire to ZA. This desire evokes in Zeir Anpin a desire to merge with Malchut in spiritual coupling (Zivug) and pour the Light of correction into her.
From the 4th part of the Daily Kabbalah Lesson 9/21/10, Shamati #96