Excerpts from a Collection of Drashas from the Author of Bilvavi Mishkan Evneh, [Rav Itamar Schwartz], pages 104-105:
"...The aravos represent the Erev Rav souls who annex themselves onto the agudah ([lulav] bundle) that is Yisrael. ...The Shulchan Aruch states in the name of the Rokeiach that on Hoshanah Rabbah, we remove the knot binding together the Four Species. Normally, the Four Species must be tied together, but on Hoshanah Rabbah, we remove the binding of the Four Species [which symbolizes a breach in our agudah achas – caused by the Erev Rav amidst us].But what causes the disconnection from amongst ourselves in the first place? What causes the disparity amongst us that we need to bind ourselves together? It is due to the presence of the souls of the Erev Rav within the Jewish people. The Sages state that Erev Rav married the women of the tribe of Shimon. They mixed with us, and their mixture into our nation breaks the unity of the Jewish people.There is the Erev Rav, and there is also a small group of Egyptian souls that converted, who are called “Erev Zeir” [whom Yosef circumcised]. The aravos of the first six days represent the Erev Zeir. The aravos of Hoshanah Rabbah represent Erev Rav; for the word “rav” is the same concept as the word “rabbah” (they both mean “many”).There are five groupings of Erev Rav, and we take five aravos on Hoshanah Rabbah. It is because on Hoshanah Rabbah, a new mixture enters us: the Erev Rav.Hoshanah Rabbah is called the “seal within a seal” (chotam b’toch chotam). On Rosh HaShanah, our decree is written, and on Yom Kippur, we are sealed. On Hoshanah Rabbah, we are “sealed within a seal”, similar to the halachah that wine must be sealed within a seal [or else it becomes yayin nesech, wine which is suspected of being used by a gentile for idol worship].Why isn’t one seal enough, though? Why it is necessary for us to have to be sealed again within the seal? “The seal of Hashem is truth”. There are levels of truth – emes (truth), and emes l’amitah, a more refined level of truth. On Hoshanah Rabbah, we are within the seal [being that we were already sealed on Yom Kippur], but we are still not sealed from the Erev Rav, because the Erev Rav connects themselves to the Jewish people; they are amidst us, so it is not enough if we are merely sealed once. Erev Rav is within the bounds (techum) of the Jewish people; thus, one seal/chotam is not enough to be sealed from them. Therefore, we need another “chotam” within the chotam”. (Chotam/techum have the same letters). That is why we need Hoshanah Rabbah to save us from the influences of the five kinds of Erev Rav....The Erev Rav corresponds to the leaves of the hoshanos which must be banged on the ground, so that the leaves fall off. This shows that we need to ‘knock off’ the ‘leaves’ of Erev Rav from amidst us. Thus, the aravos that we take on the seventh day of Succos, so that we can bang hoshanos with them, have a special role which the aravos of the first six days aren’t able to accomplish. The aravos of Hoshanah Rabbah which are banged on the ground contains the power to separate the Erev Rav from us, who wish to latch onto us. The Erev Rav is the root of all the nations of the world, which want to connect to the Jewish people. Whereas the other nations of the world are given some degree of connection with us [such as on Succos, where korbonos are brought for all 70 nations of the world], the Erev Rav may not ever be allowed into our nation.On Pesach, we left Egypt, and that was when the Erev Rav first came to mix with us. At Shavuos, right after we received the Torah, they mixed with us again to cause the sin of the Golden Calf. On Succos once again they come back once again to connect with us, but on Hoshanah Rabbah, we are given the power to separate them from amidst us. Thus, when the aravos are banged on the ground on Hoshanah Rabbah, we separate them from us by sending them back down to the earth.