The Zohar (103b) states, "Come and see: When a person sits in this abode, the shade of emunah, the Shechinah spreads out its wings over him from Above."
Reishis Chochmah (Shaar HaKedushah ch.4) writes that his Rebbe, the Remak, would only speak divrei Torah because the holiness of the succah is very great.
Mishnah Berurah (632:2) writes, "Since the kedushah of the succah is so great, it is proper that one shouldn't speak much there, other than words of kedushah and divrei Torah. Certainly, he must be cautious not to speak lashon hara, rechilus, or other forbidden words in the succah."
Bikurei Yaakov (639:2) writes, "The Shlah was very strict that one shouldn't become angry in the succah."
Yesod Yosef (ch.77) writes, "When one sits in the succah and learns and davens there, he is literally in the upper worlds."
Sfas Emes (5643) writes, "Man was created to live in Gan Eden, and this is the place of true joy, as we say (in the Sheva Brachos of a chasunah), שַׂמֵּחַ תְּשַׂמַּח רֵעִים הָאֲהוּבִים, כְּשַׂמֵּחֲךָ יְצִירְךָ בְּגַן עֵדֶן מִקֶּדֶם, 'Grant abundant joy to these loving friends, as You bestowed gladness upon Your created being in the Garden of Eden of old.' Mankind was banished from Gan Eden, but there are times when a spark of Gan Eden shines. This is why people are happy when they are in the succah. The succah is Gan Eden..."
It states (Shir HaShirim 1:4) הביאני המלך חדריו, "The king brought me into His [innermost] chambers. נגילה ונשמחה בך, "We will rejoice with You." When we are in the Succah, we are in Hashem's innermost chamber, a place of immense joy. As Chazal (Chagigah 5:) say, after the churban Beis HaMikdash, Hashem cries in His outer chambers and is happy in His innermost chambers.8
Yaaras Dvash (vol.1 drush 6) writes, "Hashem's cloud hovers over the succah. Although we don't see it, it is certain that whoever sits in the succah l’shem shamayim and learns Torah there and is happy with the Yom Tov and the mitzvos, Hashem's cloud hovers above him."9
The Pri Megadim states: One mustn't use a succah as a shortcut, and it is certainly forbidden to spit there because the succah is holy and its laws are similar to those of the Beis HaMikdash. Arizal teaches that one's table in the succah should have four legs to resemble the Shulchan of the Beis HaMikdash, which had four legs.10 Chazal consider a succah to be built on Har HaBayis, next to the Beis HaMikdash. The Gemara disproves this in the end. Nevertheless, a הוה אמינא, an initial thought of Chazal, also has significance and is indicative of the kedushah of the succah. Its holiness is like that of the Beis HaMikdash, which is built on the Har HaBayis.
When Succos falls on Friday night, some people don't say "Shalom Aleichem" (which is said before kiddush). Shem MiShmuel explains that the kedushah of the succah is so great that malachim cannot go there.11
When we say Hoshanos we call out in a loud voice הושענא שואגים הושע נא (אום אני חומה), "Hashem should save those who shout out Hosha Na." Rosh Hashanah and Yom Kippur, prayers are said in a silent voice, as we say, וכל מאמינים שהוא עונה לחש, "Everyone believes that Hashem answers silent tefillos." Reb Shalom of Belz zt'l explains that on Rosh Hashanah and Yom Kippur, we should daven silently to hide our tefillos from the malachim, the mikatrigim, who wish to prevent them from ascending to heaven. But on Succos, when we sit in the succah under the shade of the Shechinah, we are shielded from all the mikatrigim. Therefore, we can pray in a loud voice. We can shout הושע נא, and our tefillos will go up and be answered.
When Yaakov Avinu escaped from Eisav, where did he go? The Zohar (vol.3 p.100:) states that he ran to a succah. The Bnei Yissaschar (Tishrei 10:7) writes, "With the or makif, the holy light of the succah, all tumah flee from him." It is a place of holiness and protection from all bad and from all tzaros.
8 Rashi learns the opposite: that Hashem cries in the inner chambers and is happy in the outer chambers. Perhaps this can be compared to the Chovos HaLevavos (Prishus 4) הפרוש צהלתו בפניו ואבלו בלבו, that a tzaddik, "Joy is on his face, while he mourns in his heart." Our explanation above follows Rabbeinu Chananel, who says that Hashem's joy is in the inner quarters, and the distress of the Churban is expressed in the outer chambers. This is why the judgment is limited to Rosh Hashanah and Yom Kippur, but when Succos arrives, we enter the inner chamber, the place of Hashem's joy.
9 Keren l'Dovid writes, "When one sits in the succah l’shem shamayim, he feels the holiness with hislahavus. He experiences the light of the mitzvah and knows that it is true that the ענני כבוד surrounded us. This sensation cannot be explained in words, but someone who experienced it knows it's true."
One of the laws of the succah is that it must be at least ten tefachim high. The Gemara (Succah 4:) explains that this is because the Shechinah never descended below ten tefachim. The Chesed L'Avraham and the Sfas Emes (תרמ"ב ד"ה כתיב) say that this hints at the holiness of the succah. It tells us that the Shechinah resides above it.
According to halachah, a succah must be made of at least two full walls and one smaller wall, the length of a tefach. The holy sefarim explain that this represents an arm. An arm has three parts: The two larger parts of the arm and the palm. The succah, with its two large walls and one small wall, represents an arm. Keviyachol, when we sit in the succah, it is like Hashem is hugging us.
Some tzaddikim were careful that a goy shouldn’t enter the succah because of its immense kedushah.
The Chiddushei HaRim zt'l teaches that Hashem cares for us in the same manner as a mother cares for her child. On Rosh Hashanah, בלאזט מען אונז אפ, Hashem blows on us and blows away our impurities. On Yom Kippur וואשט מען אונז אפ, Hashem rinses us off, as it says, וזרקתי עליכם מים טהורים, "I will throw onto you purifying waters" (Yechezkel 36). And on Succos, דעקט מען אונז צו, Hashem covers and swaddles us.
Similarly, the Ohev Yisrael (Likutim) says that a chicken first feeds its chicks and then covers them under its wings. This is how the Shechinah interacts with us during these days. On Rosh Hashanah, Hashem gives us parnassah, and on Succos, Hashem takes us under His wings.
10 We repeat this not necessarily so that people should go out and buy a table with four legs, but rather to highlight the holiness of the succah, which resembles the Beis HaMikdash.
11 Before each meal, there is a custom to invite the Ushpizin to the succah אברהם, יצחק, יעקב, משה, אהרן, יוסף, ודוד. The question was raised (for those who say Shalom Aleichem in the succah on Friday night) which should be recited first: Should we first invite the Ushpizin, or should we first greet the malachim and begin with Shalom Aleichem?
Someone told the Satmar Rebbe zt'l that he thinks we should invite the malachim first because the rule is תדיר ושאינו תדיר תדיר קודם, whatever is more frequent comes first. Shalom Aleichem is recited every Friday night and should, therefore, be said first.
The Satmar Rebbe replied that although Shalom Aleichem is said each week, different malachim come each week. This is because the level of malachim that accompany us on Shabbos night depends on the person’s deeds during the week and on the amount he prepared himself during the week for Shabbos. Therefore, said the Satmar Rebbe, the ushpizin and the malachim are equally תדיר. The question thus remains which one should be invited into the succah first: the malachim or the Ushpizin?
The Satmar Rebbe said, "In my opinion, the Ushpizin should be invited first because the Ushpizin are tzaddikim, and tzaddikim are greater than malachim."