Guests, and they are the souls of the seven forefathers: Abraham, Isaac, Jacob, Joseph, Moses, Aaron, and David. Each day one is invited into the Sukkah. In order to merit in having the spiritual guests, one should invite physical guests as well.
(יב) דָּבָר אַחֵר, פְּרִי עֵץ הָדָר, אֵלּוּ יִשְׂרָאֵל, מָה אֶתְרוֹג זֶה יֵשׁ בּוֹ טַעַם וְיֵשׁ בּוֹ רֵיחַ, כָּךְ יִשְׂרָאֵל יֵשׁ בָּהֶם בְּנֵי אָדָם שֶׁיֵּשׁ בָּהֶם תּוֹרָה וְיֵשׁ בָּהֶם מַעֲשִׂים טוֹבִים. כַּפֹּת תְּמָרִים, אֵלּוּ יִשְׂרָאֵל, מָה הַתְּמָרָה הַזּוֹ יֵשׁ בּוֹ טַעַם וְאֵין בּוֹ רֵיחַ, כָּךְ הֵם יִשְׂרָאֵל יֵשׁ בָּהֶם שֶׁיֵּשׁ בָּהֶם תּוֹרָה וְאֵין בָּהֶם מַעֲשִׂים טוֹבִים. וַעֲנַף עֵץ עָבֹת, אֵלּוּ יִשְׂרָאֵל, מָה הֲדַס יֵשׁ בּוֹ רֵיחַ וְאֵין בּוֹ טַעַם, כָּךְ יִשְׂרָאֵל יֵשׁ בָּהֶם שֶׁיֵּשׁ בָּהֶם מַעֲשִׂים טוֹבִים וְאֵין בָּהֶם תּוֹרָה. וְעַרְבֵי נָחַל, אֵלּוּ יִשְׂרָאֵל, מָה עֲרָבָה זוֹ אֵין בָּהּ טַעַם וְאֵין בָּהּ רֵיחַ, כָּךְ הֵם יִשְׂרָאֵל יֵשׁ בָּהֶם בְּנֵי אָדָם שֶׁאֵין בָּהֶם לֹא תּוֹרָה וְלֹא מַעֲשִׂים טוֹבִים, וּמָה הַקָּדוֹשׁ בָּרוּךְ הוּא עוֹשֶׂה לָהֶם, לְאַבְּדָן אִי אֶפְשָׁר, אֶלָּא אָמַר הַקָּדוֹשׁ בָּרוּךְ הוּא יֻקְשְׁרוּ כֻלָּם אֲגֻדָּה אַחַת וְהֵן מְכַפְּרִין אֵלּוּ עַל אֵלּוּ, וְאִם עֲשִׂיתֶם כָּךְ אוֹתָהּ שָׁעָה אֲנִי מִתְעַלֶּה, הֲדָא הוּא דִכְתִיב (עמוס ט, ו): הַבּוֹנֶה בַשָּׁמַיִם מַעֲלוֹתָו, וְאֵימָתַי הוּא מִתְעֲלֶה כְּשֶׁהֵן עֲשׂוּיִין אֲגֻדָּה אַחַת, שֶׁנֶּאֱמַר (עמוס ט, ו): וַאֲגֻדָּתוֹ עַל אֶרֶץ יְסָדָהּ, לְפִיכָךְ משֶׁה מַזְהִיר לְיִשְׂרָאֵל: וּלְקַחְתֶּם לָכֶם בַּיּוֹם הָרִאשׁוֹן.
(12) Another explanation: "The fruit of a beautiful tree" - these are [referring to] Israel. Just like this citron (etrog), which has taste and has smell, so too Israel has among them people that have Torah and have good deeds. "The branches of a date palm" - these are [referring to] Israel. Just like this date, which has taste and has no smell, so too Israel has among them those that have Torah but do not have good deeds. "And a branch of a braided tree (a myrtle)" - these are [referring to] Israel. Just like this myrtle, which has smell and has no taste, so too Israel has among them those that have good deeds but do not have Torah. "And brook willows" - these are [referring to] Israel. Just like this willow, which has no smell and has no taste, so too Israel has among them people that have no Torah and have no good deeds. And what does the Holy One, blessed be He, do to them? To destroy them is impossible, but rather the Holy One, blessed be He, said "bind them all together [into] one grouping and these will atone for those." And if you will have done that, I will be elevated at that time. This is [the meaning of] what is written (Amos 9:6), "He Who built the upper chambers in the heavens" (indicating his elevation). And when is He elevated? When they make one grouping, as it is stated (Ibid.), "and established His grouping on the earth." Hence Moshe warned Israel, "And you shall take for yourselves on the first day."
תלמוד בבלי מסכת סוכה דף כז עמוד ב
וחכמים אומרים: אף על פי שאמרו אין אדם יוצא ידי חובתו ביום טוב הראשון בלולבו של חבירו, אבל יוצא ידי חובתו בסוכתו של חבירו, דכתיב +ויקרא כג+ כל האזרח בישראל ישבו בסכת - מלמד שכל ישראל ראוים לישב בסוכה אחת.
TB Sukkah 27b
The sages say “even though a person cannot exempt himself from his obligation of the four species on the first day of sukkot with a borrowed lulav and etrog, he may exempt himself from his obligation of sitting in a sukkah by using his friend’s sukkah. The basis for this is the verse that says “every citizen of Israel shall sit in sukkot”. This teaches us that all of Israel are fit to sit in one sukkah.
כיצד הקטנים נותן להם קליות ואגוזים ומגדנות. והנשים קונה להן בגדים ותכשיטין נאים כפי ממונו. והאנשים אוכלין בשר ושותין יין שאין שמחה אלא בבשר ואין שמחה אלא ביין. וכשהוא אוכל ושותה חייב להאכיל לגר ליתום ולאלמנה עם שאר העניים האמללים. אבל מי שנועל דלתות חצרו ואוכל ושותה הוא ובניו ואשתו ואינו מאכיל ומשקה לעניים ולמרי נפש אין זו שמחת מצוה אלא שמחת כריסו. ועל אלו נאמר זבחיהם כלחם אונים להם כל אוכליו יטמאו כי לחמם לנפשם. ושמחה כזו קלון היא להם שנאמר וזריתי פרש על פניכם פרש חגיכם.
Rambam original source:
Mishneh Torah, Yom Tov (Rest on A Holiday) 6:18:
How [does one make everyone happy appropriately]? Give the children nuts and candy, and buy the women as much nice clothing and jewelry as he can afford. And the men eat meat and drink wine since there is no happiness without meat and wine. And when [the head of household] eats and drinks, he is obligated to feed strangers, orphans and widows as well as all other poor people. However, if he locks his doors and eats and drinks with his family and does not feed the poor and others going through hard times, this is not the joy which was commanded, but [merely] satisfying his stomach. About such people, it is said "There sacrifices are like the bread of mourners, all who eat it will be contaminated for their bread is for their own appetites." Such parties are disgraceful to those who participate in them as it says "I will spread dung on your faces, the dung of your festival [sacrificial meals]"
If he used an animal as a wall of the Sukkah, R. Meir declares it invalid and R. Judah valid, for R. Meir was wont to say, Whatever contains the breath of life can be made neither a wall for a Sukkah, nor a side-post for an alley nor boards around wells, nor a covering stone for a grave. In the name of R. Jose the Galilean they said, Nor may a bill of divorcement be written upon it. What is the reason of R. Meir? — Abaye replied, Lest it die. R. Zera replied, Lest it escape. Concerning an elephant securely bound, all agree [that the Sukkah is valid], since even though it die, there is still ten [handbreadths height] in its carcass.
Regarding what then do they dispute? Regarding an elephant which is not bound. According to him who says, Lest it die, we do not fear; according to him who says, We fear lest it escape, we do fear. But according to him who says, Lest it die, let us fear also lest it escape? — Rather say, Regarding an elephant which is not bound, all agree [that the Sukkah is invalid];
Regarding what do they dispute? Regarding an [ordinary] animal which is bound: According to him who says, Lest it die, we fear [for that] according to him who says, Lest it escape, we have no fear.
But according to him who says, Lest it escape, let us fear lest it die? — Death is not a frequent occurrence. But is there not an open space between the animal’s legs? [It refers to] where he filled it in with branches of palms and bay-trees. But might it not lie down? — [It refers to] where it was tied with cords from above. And according to him who says, Lest it die, is it not tied with cords from above? — It may occur that it is made to stand within three [handbreadths] of the covering but when it dies, it shrinks, and this might not enter his mind…