Our liturgy for each of the Shalosh Regalim makes specific mention of the relevant holiday and the phrase that captures that holiday's essence. Pesach is called Z'man Cheiruseinu, marking our freedom from Mitzrayim. Shavuos is called Z'man Matan Toraseinu, commemorating our receipt of the Torah. Z'man Simchaseinu, however, the description we associate with Succos, doesn't seem to capture any event specific to the yom tov. Why does Succos bear this description?
One could posit that based Succuos receives this description because, in the Torah's list of the yomim tovim in parashas Emor, the word "simcha" appears exclusively in conjunction with Succos (Vayikra 23:40) . Moreover, when the Torah reviews the yomim tovim in Re'eh, the word "simcha," though it appears once regarding Shavous, appears twice regarding Succos (Devarim 16:14-15), for a total of three appearances. It seems, therefore, that our tefillos simply reflect the choice of word in the Torah. But why does the Torah itself associate Succos with simcha more than the other yomim tovim? What makes Succos a greater source of joy than any other yom tov?
The very first Mishnah in Maseches Succah rules that a succah higher than 20 amos is passul for use on Succos. The Gemara offers three sources for the Mishnah's ruling: Rabbah attributes the ruling to the passuk in Emor (23:43) that gives the reason for the mitzvah of dwelling in the sucah: "So that your generations will know that I gave b 'nei Yisrael booths in which to dwell when I took them out of the land of Mitzrayim; I am Hashem, your Lord." Rabbah explains that one can only achieve this "knowledge" if the succah is no higher than 20 amos, for if the schach is above 20 amos, it will be out of sight. (If one dwelling in the succah cannot see the schach, it cannot serve its function as a constant reminder of the succos in the desert.) Rabbah's position explains why a succah more than 20 amos high is passul, but we are still left unclear as to the reason that knowledge is an essential portion of the mitzvah. Before we address this question, we must first examine the other two explanations in the Gemara.
R' Zeira bases the 20-amah height limit on a passuk in Yeshaya (4:6) that indicates that the purpose of a succah is forshade, explaining that in order to fulfill one's chiyuv to dwell in the succah, one must dwell in the shade of the succah . The taller the walls, the more they block the rays of sunlight. If the succah is too high, more than 20 amos high, to be precise, the main source of shade will be the walls, not the schach. R' Zeira's opinion also needs explanation, for the walls are as intrinsic to the succah as the schach - after all, a sucah without walls is just as passul as a suecah without schach (see Shu1chan Aruch §630). Why, then, is the shade of the walls invalid to fulfill the requirement of shade?
Rava offers yet a third source for the height requirement. The passuk in Emor (Vayikra 23:42) tells us to live in Succos for seven days. Rava elaborates: "Leave your permanent home and dwell in a temporary dwelling." A temporary home, by definition, cannot be higher than 20 amos. Rava's opinion leaves us somewhat confused as well, not explaining why exactly the Torah says that the succah must be temporary? Moreover, the language of the Gemara seems odd. Wouldn't it have been sufficient to simply say, "Live in a temporary home?" What does Rava mean to add when he says, "Leave your permanent home"?
Understanding Rava's explanation more clearly will provide us with an insight into the yom tov of Succos with which we can further explain the other opinions in the Gemara. When Rava says, "Leave your permanent home," he is not merely giving us directions to the temporary abode. In order to live in a temporary home, one must obviously vacate his permanent home first. Rather, Rava teaches that one must perform two distinct acts, each representing a highly significant aspect of Succos. First, one must abandon his permanent home. Then can he enter his temporary dwelling. Only thus has the mitzvah been fulfilled.
In the Shabbos zemirah Yedid Nefesh, we beseech Hashem to spread His "succas shalom, shelter of peace," over us. The Yesod Malchus explains that this shelter is of a divine, spiritual nature and is manifested in the form of hashgacha pratis Divine Providence. In other words, we request that Hashem give us siyata dishmaya. How does a succah symbolize Divine Providence? Based on Rava's position regarding succah, we can conjecture that leaving one's permanent, secure household for a temporary hut epitomizes one's reliance on Hashem. After all, to, whom but Hashem can an individual, so clearly vulnerable to the elements, tum for support? As such, the succah emerges as the symbol of bitachon and Divine Providence, par excellence.
Rava teaches us that the essence of Succos is this lesson in bitachon, the act of dwelling in the temporary succah, realizing our total dependence on Hashem. The sucah must be temporary, for if it would be permanent, we would feel secure in its permanence to the point of forgetting, chas v'shalom, the Source of our protection and tranquility. Consequently, the succah cannot be higher than 20 amos.
Looking back at our Gemara, we can now understand Rabbah's position. Rabbah explained that the succah must be no greater than 20 amos so that the dweller can see the schach above him and recognize that he is in a succah. We now understand the reason behind the necessity of this recognition: the whole point of the succah is the valuable lesson in bitachon gained from dwelling in it. Conscious recognition of our vulnerability, i.e. the knowledge that one is dwelling in a sucah, is a must for this recognition.
Even R' Zeira's opinion is now clear. There is a fundamental difference between the shade of the schach and the shade of the walls, because al pi halacha there is a fundamental difference between the schach itself and the walls themselves. The halacha is that the walls of the succah unlike the schach, may be constructed or any material, even material of a permanent nature (see Shu1chan Aruch §630). According to Rav Zeira, the essence of the succah is the shade, as it is the shade of the schach that teaches us to put our trust in Hashem. Therefore, Rav Zeira emphasizes that one must dwell in the shade of the schach, to the exclusion of the shade of the walls. It is also clear why the halacha mandates that the schach be made of temporary material. The same way a permanent succah does not help teach us reliance on Hashem, schach of a permanent nature also fails to convey the message of bitachon.
Our theory also answers our original question regarding the relationship between Succos and simcha. A person caught up in the mundane gains a certain level of security and trust in himself and his own ability. He builds himself an extravagant house, buys expensive cars, purchases designer clothing, and may even go all out to acquire certain cheftzei mitzvah. But he is not necessarily happy. Only when one realizes that all his possessions are really gifts from Hashem can he be truly happy. The difference is clear: if a person receives a gift from a friend, he is certainly pleased. But how much more excitement and appreciation would he feel if he received this gift not from his friend, but from the king. How excited and appreciative would we be if we truly realized that everything we have is a gift from the King of Kings.
On Succos we are commanded to leave our permanent homes and live in a temporary home, to realize our vulnerability and to internalize the lesson that we must trust in Hashem. The same way a helpless baby feels happily secure in its mother's arms, we will find true joy in the knowledge that we are truly protected in the hands of our Father in Heaven.