The Inner Meaning Behind The Four Species and the Sukkah
In the Yom Tov of Sukkos, the main mitzvos are to shake the four species and to sit in the sukkah. (There used to also be the mitzvah of nisuch hamayim in the Beis Hamikdash, but we no longer have the Beis Hamikdash).
The mitzvah of the four species involves movement – we shake them and move them around, which symbolizes how we want to move away from evil, and instead to come closer to Hashem. By contrast, the mitzvah of sitting in the sukkah involves no movement at all – we sit in it and don’t move at all. This symbolizes a different aspect of our avodas Hashem: to reach the point of “non-movement.”
In other words, there are two steps in our avodas Hashem- sometimes we have to “move”, and sometimes we “don’t move”.
Sukkos of Today and Sukkos of the Future
There is a halachah on Sukkos that we have to sit specifically in the “shadow” (“tzeil”) of the sukkah. This is the sukkah of nowadays – we sit in the sukkah’s shadow, which symbolizes how Hashem’s radiance is concealed from us.
However, in the future, Chazal state that the sukkah will be made from the skin of the leviathan – it will be a sukkah of entirely light. The Sukkah of the future will be the perfect sukkah, in which “all citizens” (“kol ha’ezrach”) will be enveloped within it; “ezrach”, “citizen”, is rooted in the word “zerichah”, “light.” This alludes to the sukkah of the future, which will be totally light. This is because the depth behind the sukkah is not just to be “in the shadow” of the sukkah, but to sit in the light of Hashem.
Dovid Hamelech says that “Hashem is my light, and my salvation.” Chazal expound on this verse that “my light” is referring to Rosh Hashanah, while “my salvation” is referring to Yom Kippur. Sukkos, which is the continuation of this, is the actual revelation of “my light”, Rosh Hashanah – which is entirely Hashem’s light.
It is only nowadays that the sukkah is like a “shadow”, because since there is evil in the world, the evil places a “shadow” on the “light” of Rosh Hashanah and dims it from its full effect. But in the future, there will be no more evil, and then Sukkos will no longer be a concept of shadow, but rather a concept of complete spiritual light.
Shemini Atzeres – The D’veykus With Hashem Above All Spiritual Light
Even higher than Sukkos is the level of Shemini Atzeres, which is the day of complete unity between Hashem and the Jewish people. It is a power that is above even the spiritual light revealed through Rosh Hashanah and Sukkos.
Chazal say of this day that Hashem said, “Remain with me one more day”. This is the great desire of Hashem toward His people, and it was there even before Hashem created light on the first day; this great desire that He has to us returns on Shemini Ateres.
 The Rav has been brief here in this fundamental concept; we will elaborate here to give more background. Generally speaking, the lower mode of Avodas Hashem involves movement, such as the six days of the week, when we move and work, representing the mundane. On Shabbos we don’t move, because we do not work; thus non-movement is always seen as the higher aspect of our Avodas Hashem. In sefer Da Es Menuchasecha (which is available online in English as The Search for Serenity), these concepts are explained at length in regards to achieving menuchas hanefesh – that the more we reach our “non-moving” state of our soul, the closer we come to our inner peace. The innermost part of our soul, our Yechidah, is a non-moving part of our existence, because our actual self is very still, content with its existence, for it is a cheilek eloka mimaal, a “portion of Hashem”. Our very essence is unmoving because it is rooted in Hashem, who is unmoving. Non-movement is also explained more in sefer Bilvavi Mishkan Evneh: Shabbos Kodesh, as well as in sefer Da Es Hargoshosecha (soon to be released in English as “Getting To Know Your Feelings”). This footnote does not nearly exhaust the topic; it is a very vast subject which the Rov frequently discusses, and the references we have given here are the main sources where the Rov discusses it at length.
 Editor’s Note: See sefer Sifsei Chaim: Moadim (Vol. I) who explains how the spirituality of Shemini Atzeres is deeper than the first days of Sukkos. On Sukkos, we have the mitzvah of sukkah and the four species, because we are given these tools on Sukkos to reach closeness to Hashem through them. However, Shemini Atzeres is a higher connection we have with Hashem, as it is the culmination of the entire Yomim Noraim; thus, it doesn’t require us to sit in the sukkah or to shake the four species, because it is more of a direct connection with Hashem.