The Symbolism of Sukkot
A. Two Mitzvot
There are two distinct mitzvot associated with Sukkot, with no immediately apparent connection between them: the obligation to live in a sukka, a temporary booth with a roof made of branches or other material of vegetable origin, and an obligation to "take" four special species (and shake them) - the etrog (citron fruit), the lulav (palm branch), the hadas (myrtle branch), and the arava (willow branch). Since the first has an explicit rationalization given in the Torah, and has also lent its name to the holiday - it is called by the Torah "the Festival of Sukkot" (the plural of sukka) - we shall first concentrate on it.
B. The Sukka
The Torah states:
You shall dwell in sukkot for seven days, every member of (the community of) Israel shall dwell in sukkot; in order that your generations shall know that I settled (cause to dwell) the Jews in sukkot when I brought them out of Egypt, I am HaShem, your God. (Lev. 23:42)
The meaning of the word "sukka" or "sukkot" is not as clear as we would like to think. The root SKH means to cover and protect. Clearly, the mitzva refers to some sort of structure in which one can dwell. The Talmud cites verses to prove that the most important part is the roof. However, there is an interesting disagreement in the Talmud concerning the reference of the "sukka" in which the Jews dwelled in the desert when they left Egypt.
"That I settled the Jews in sukkot when I brought them out of Egypt" - these were the clouds of glory. This is the opinion of R. Eliezer.
R. Akiva says: They made actual sukkot (booths). (Sukka 11b)
R. Eliezer claims that the booths which we build today commemorate not similar booths built by the Jews three thousand years ago, but a direct spiritual protection miraculously provided in the desert by God - clouds of glory, meaning a visible symbol of God's presence and providence. Interestingly, although this disagreement does not appear to be a halakhic one, the Rambam, in his halakhic code, nonetheless cites R. Eliezer's opinion as being authoritative.
I do not think that there is a great distinction, in terms of what the message and inner meaning of the sukka is about, between R. Akiva and R. Eliezer. Why does God want us to remember that we dwelled in booths when He took us out of Egypt? A better question might be: What is important about remembering the desert experience in general (recalling that there is another festival - Passover/Pesach - devoted to remembering the exodus from Egypt itself)? The answer to this question is given by the Torah itself.
You should remember the entire path that God led you for the last forty years through the desert... in order to teach you that man does not live by bread alone, but on that which comes from the mouth of God does man live. Your clothes did not wear away, nor your feet blister, for these forty years. (Deut. 8:2-4)
Lest your heart be raised up and you forget HaShem your God, who took you out of the land of Egypt, the house of bondage; who led you through the great and terrible desert, snake, serpent and scorpion, and a thirst without water, who brought you out water from the stone of flint; who fed you manna in the desert... (8:14-16)
R. Akiva's explanation - that the sukkot were desert booths, and R. Eliezer's explanation - that they were clouds of Divine glory, are actually two opposite sides of the same coin. The point is that in the desert the Jews were not living in well-designed structures with central climate control and a well-stocked larder. Objectively, they were living in the "great and terrible desert," a place without water, a place of death - "snake, serpent, and scorpion" - at best living only in flimsy booths that any desert storm could blow to the sea. In truth, their only protection was not natural, but the hand of God, an island of life in a framework of death, formed not by great dikes or walls, but by the Presence of God, by the clouds of glory.
The booths of R. Akiva, then, are to be understood as "MERE BOOTHS" - in other words, as insubstantial, inadequate protection in natural terms. R. Eliezer concentrates on the positive side, which R. Akiva's explanation highlights by its failings - the Jews in the desert lived IN THE HAND OF GOD, literally, eating (manna), drinking (the water from a stone), and sleeping (the clouds of glory) in total security without relating to the natural environment.
The sukka, the one we move to for seven days, is therefore defined halakhically by contrast with our regular domicile. The defining halakhic characteristic of a sukka is "dirat ara'i" - a temporary dwelling. It is defined IN CONTRAST to our home. We leave the comfort and security of our homes and place ourselves, at least symbolically, in God's hands.
C. Some Laws
There are two sets of laws relating to the physical attributes of the sukka - the walls, and the roof.
1. The walls: Somewhat surprisingly, a sukka requires only a minimum of two walls, plus the beginning of the third. It would be hard to call such a structure a house. The minimum size is 7 tefachim square - about 65 cm. (26 inches) on each side. This is sufficient for most of one's body and a small platform to eat from. The minimum height is 10 tefachim (95 cm. - 40 inches), which is enough to sit on the floor (but please do not stand up).
Incidentally, in case you think that this is all highly theoretical, I have used both measurements - though not at the same time. When I first moved to Israel, my sukka was on my porch, which projected exactly 80 centimeters beyond the porch above. Since the part covered by my upstairs neighbor's porch could not be included in the sukka, I had only slightly more than the minimum width in which to eat - I had to draw a line on the floor to make sure that I did not overextend myself while munching on the holiday kugel. Nowadays, I have a huge sukka outside my house, suitable for feasting with my family and invited guests. But, I also build a small sukka off my bedroom for sleeping. In that case, I simply lay branches on the railing of the bedroom balcony, and, that's right! - it is exactly one meter high. When I put my bed in there, the only way to get in is by crawling, keeping my head low so as not to destroy the roof.
2. The roof. The covering of the sukka, called "sekhakh" (same root as the word "sukka"), bears the most halakhic scrutiny. Sekhakh must be made of vegetative matter, and must be in a natural form, that is, not made into a utensil. At the same time, it must be cut down, and not still growing, which is why you cannot build a sukka under a tree. It must be sufficient to produce "more shade than sun," but should not be perfectly solid, which would make the sukka into a permanent dwelling. Practically speaking, this means that when it rains the sukka is unusable.
D. The Experience
What does all this add up to? The experience of sukka is one of LEAVING OUR WELL-ENDOWED HOMES AND MOVING OUT, EXPOSED TO NATURE, without the usual man-made security with which we surround ourselves. Although the cold climates of Northern Europe and America have led to a general limitation of sukka to eating only, the mitzva is to DWELL in a sukka, which includes eating, sleeping, reading - everything you would usually do in your house. (In Israel it is quite common to sleep in the sukka, which is why I have three - one for eating, one for my sons to sleep, and one for me to sleep. Most people, I suspect, do all three in the same structure.)
What is the positive side of this negatively-defined experience? This is what R. Eliezer is trying to emphasize. This is not really a back-to-nature experience, at least not in the usual sense. Once a year, we return to the experience of the Jews in the desert, which was one of being totally in the hands of God, cared for directly by Him, and not relying on our artificial means of creating our own environment. The sukka represents the negation of human artifice in order to recreate the experience of direct sustenance from God. In other words, living in the sukka means living within God's hands, being totally in God's presence, not in the manner of going to the synagogue or the Temple - where I enter a special holy realm divorced from this world - but as part of this world. One can live here and now, eat, drink, and sleep, under God's clouds of glory. The Divine Presence is within the world. In other words, as the verse quoted above concludes, "Man does not live by bread alone, but by that which comes out of the mouth of God."
This is reflected in a curious law. It is prohibited to use any part of the sukka during the holiday for some other purpose. This extends even to the decorations hung in the sukka. The explanation given in the Talmud (Sukka 9a) implies that the sukka has the status of "hekdesh" - a sacred object. This cannot be literally true, but must be understood as a kind of temporary sanctity, derived from the mitzva. This status is unique, applying to no other mitzva (well, remind me before Chanuka to compare this to the oil in the Chanuka lamp). I think the reason is that the physical structure of the sukka symbolizes, or rather encapsulates, the presence of God.
An old Chassidic saying reflects this idea very well. There are two mitzvot which envelope a Jew totally. One is Shabbat, since it is a mitzva of time. The other is sukka, a mitzva of space. You are living in mitzva by breathing, as it were, in the sukka. Just by living, by being there, one is immersed in sanctity. There is no other mitzva like it.
E. Lulav and Etrog
The meaning of the four species which we take on Sukkot is more enigmatic. There are many ideas found in rabbinic literature, but I wish to touch only on one. The Torah says about the four species that,
On the fifteenth day of the seventh month, when you are gathering in your produce of the earth, you shall celebrate a celebration of God for seven days... And you shall take for yourselves on the first day the fruit of a beautiful tree (etrog), palm branches, the branch of a thick tree (myrtle, hadas), and brook-willows, and you shall rejoice before God for seven days. (Lev. 23:39-40)
It is clear that the four species are a form of rejoicing and celebration. The only verb used by the Torah to describe what we do is to "take" them and "rejoice before God." Indeed, the Torah mandates a special level of joy on Sukkot not found on other festivals.
Celebrate the Festival of Sukkot for seven days, when you gather in from the grain and the vine. And you shall rejoice on your festival, you, your son, your daughter, your manservant, and your maidservant, and the Levite, the stranger, the orphan, and widow who live in your gates... and you shall be only joyful. (Deut. 16:13-16)
The Rambam rules:
Even though there is a commandment to rejoice on all the holidays, there was, in the Temple, extra joy on Sukkot... It is a mitzva to increase this joy. The joy that a man rejoices in the performance of a mitzva and in the service of God is a great service, and one who holds himself back from this joy is deserving of punishment... There is no dignity or honor other than to rejoice before God... (Hilkhot Sukka 8:12-16)
The crucial phrase here, both in the Rambam and in the original Torah verses, is "before God." The additional joy of Sukkot derives directly from the fact that the entire holiday is an experience of being "before God," in God's presence. Normally, this is associated with being in the Temple in Jerusalem, and on Sukkot as well, the highest fulfillment of this joy would be in the Temple area. But on Sukkot we discover the possibility of being in God's presence anywhere, even the desert. In fact, that was the main purpose of the long forty-year sojourn of the Jews before being allowed to enter the promised land - to learn that land, house, fields, jobs, buildings, careers, etc., are not to separate us from God, replace Him and His providence by providing a "more substantial" form of security. Even in this world, there is an experience of being in God's immediate presence, without any mediation. That results in joy - for there is no other joy other than being in the presence of God. The lulav and etrog, waved before us during prayers, are one expression of that joy. The week-long celebrations in the Temple were another.
F. Shemini Atzeret
Sukkot has an eighth day, called Shemini Atzeret (and Simchat Torah, the extra ninth day outside of Israel). Actually, Shemini Atzeret is considered to be a different distinct holiday, which is why lulav and sukka do not apply. (Outside of Israel, many have the custom of eating in the sukka on Shemini Atzeret but without reciting a blessing. However, this is not the essential law, but rather due to uncertainty as to whether this is really the seventh day of Sukkot.) But clearly, Shemini Atzeret is connected to Sukkot, which is what its name means - the assembly of the EIGHTH DAY. This holiday has no particular character, no characteristic mitzva, other than to rejoice. (The celebration of Simchat Torah, the completion of the year's Torah reading, is a relatively late custom.)
In light of the meaning of Sukkot, the inner nature of Shemini Atzeret is clear. On Shemini Atzeret, we return from the sukka (our "temporary dwelling") to our homes. The desert too was meant to be a temporary existence. Living solely and directly in God's hands, without the mediacy and the challenge of making our own worlds, is a rarefied experience. It represents the highest joy, the most sublime celebration - but it is meant as a preliminary to the more prosaic but essential task of living properly, of celebrating our daily work and approach to God, from below, as one works the Land of Israel and serves God on one's own land. This is the necessary conclusion to Sukkot - you come back to this world, to your own man-made world, and remain, somehow, before God, in joy. It is, indeed, only fitting that on this day we also begin again a cycle of Torah reading, starting again another year.