Avos chapter 3, mishnah 4 (in some versions it is numbered as mishnah 3). Rabbi Shimon presents two sides of one and the same meal:
"Sheloshah she'achlu al shulchan echad velo amru alav divrei Torah, ke'ilu achlu mizivchei meisim, shene'emar: 'Ki kol shulchanos malu ki tzoah beli makom'" - three who eat together at one table and do not speak words of Torah among themselves are as if they had eaten from offerings brought to the dead.
"Aval sheloshah she'achlu al shulchan echad ve'amru alav divrei Torah, ke'ilu achlu mishulchano shel Makom baruch Hu, shene'emar: 'Vayedaber elai zeh hashulchan asher lifnei Hashem'" - three who eat together and say words of Torah at their table are as if they had eaten from the table of the Holy One, blessed is He.
Two basic premises:
Three constitute a group: when three Jews gather together, a chaburah, a group, is formed. This finds its most striking halachic expression in the obligation of zimun, and the Malbim explains that the general principle of "berov am hadras melech", that the king's honor is revealed within a multitude, takes effect from the moment there are three. This means that three together are greater than the sum of their parts, and they must function in harmony as a group, bringing out the best in one another and accomplishing what none of them could accomplish alone. Hence, when three gather, a special opportunity is given to do something elevated, and wasting it is a great loss.
Everything has a spiritual root: the kabbalists, foremost among them Rabbi Chaim Vital in the name of his teacher the Arizal, teach that everything in this world has a physical expression and also a spiritual root. When a person connects to the spiritual root and raises the physical along with it, he is connected to life, to eternal life and to good, and this is "uvacharta bachaim". But when he focuses on the physical part alone, cut off from its spiritual root, that is death, decay and destruction, and distance from Hashem.
The mizbei'ach - the elevation of all the elements of creation:
The place where the physical world is elevated in the most direct and explicit way is the Beis HaMikdash, and within it the outer mizbei'ach, which is the primary altar. There all the elements of creation are elevated through their connection to Hashem. In the basic Jewish outlook there is a hierarchy of four levels of existence:
Inanimate matter.
Plant life.
Animal life.
The speaking being, man.
On the mizbei'ach all four of these elements are elevated:
Man: the kohanim and Leviim who perform the service and sing, as well as the owner on whose behalf the offering is brought, are elevated through this service.
Animal: the animal itself, which is the offering.
Plant: the menachos, whose basis is flour and oil, and the libations, which are wine. These are considered the most important elements of the plant world.
Inanimate: the salt. There is a mitzvah from the Torah, the covenant of salt, that every offering be dipped in salt before being placed on the mizbei'ach. Salt comes from the inanimate world, and it too is elevated. Moreover, salt does not spoil, and therefore it is a symbol of the covenant between us and Hashem, a covenant that remains fresh forever and never spoils.
The table as a mizbei'ach:
When a person eats at his table, and especially at the Shabbos table, which is the very purpose of the day, he takes those same elements and elevates them. The table at which one eats parallels the mizbei'ach exactly, and as we will see, this is expressly derived in the mishnah and in the verses it cites. Around the Shabbos table the members of the household sit, speak words of Torah and sing zemiros, and there you have the elevation of the speaking being; they eat the finest meat and fish, thereby elevating the animal; they drink wine and break bread, elevating the plant world.
Finally, many have the practice of dipping the bread in salt at the table, in order to remind themselves that the table functions as a mizbei'ach. The bread no longer needs salt for the sake of its taste, for if it needed salt, it would have been added into the dough; rather, it is tasty as it is. The dipping in salt is therefore done as though the bread were an offering. Every time a person dips his bread in salt at the Shabbos table, and at every meal, that dipping should serve as a reminder that the food is like an offering, and that he is there to elevate the physical world and connect it back to Hashem, and through this he himself is elevated.
Two Ways of Eating:
In light of this, a person who sits down to eat faces two possibilities. He can eat in order to indulge the physical side of his body and satisfy his bodily needs alone, which is the very opposite of elevation, since eating of that sort drags a person downward. Alternatively, he can use the experience of eating as an opportunity to gain strength for serving Hashem, and to raise up with him the elements of the food, and then it becomes an uplifting experience. The Mishnah teaches that when a person gathers together with two others, so that now there is a group here, a uniquely special opportunity is given to him. To squander it on filling his stomach and indulging his bodily needs alone, with no awareness of the soul's elevation, is a terrible disgrace, turning the entire meal into an animalistic and repulsive experience instead of a holy and uplifting one.
It is worth noting that the word "lechem", which means food, shares a root with "milchamah", war. For the war a person wages every time he sits down to eat is this: will he be like an animal filling its belly, or will he be the exalted creature that he truly is as a human being, raising up the food he eats for the service of the Holy One, blessed is He.
A Careful Reading of the Mishnah's Wording:
The Mishnah says "sheloshah she'achlu al shulchan echad" - three who ate at one table. The very fact that three are eating together shows that they have time on their hands, for had they been in a hurry they would not have eaten together, and each one would have worried that his fellow would delay him at Bircas HaMazon. And if that is the case, and nevertheless "lo amru alav divrei Torah" - they did not say words of Torah over it, this is a missed opportunity. It should be added that Chazal warned against speaking during the actual act of eating because of the danger involved, and one must be careful that his mouth be clear of food. Therefore, either we are dealing with a lengthy meal in which one eats while his fellow speaks, or the Mishnah uses the past tense, "she'achlu", "who ate", to teach that once they have finished eating, then they should say words of Torah.
"Zivchei Meisim":
The expression "zivchei meisim" alludes to the verse (chapter 106, verse 28): "And they attached themselves to Baal Pe'or and ate the offerings of the dead", meaning that they attached themselves to that idol and ate from its offerings, which are the offerings of the dead. Idolatry is called "dead" because there is no life in it and it cannot respond, in contrast to the Holy One, blessed is He, who is called "the living God".
And since the table is like an altar, the foods upon it are like offerings. When the eating is meant to serve the person and his needs alone, with nothing in it for the sake of anything higher than himself, these are like the offerings of idolatry. For this is the entire essence of idolatry: a way of manipulating things in order to obtain what a person wants.
The Verse in Yeshayahu:
Regarding this, the Mishnah brings the verse from Yeshayahu: "ki kol shulchanos male'u ki tzo'ah beli makom" - for all the tables are full of vomit and filth, without space. From the context of the preceding verse it emerges that the prophet is speaking of people who hold licentious meals steeped in indulgence: "And these too erred through wine and strayed through strong drink" - they sit at their tables drinking wine and intoxicating beverages, erring and losing their way. Then our verse comes and says that those tables, where the experience of eating serves only to satisfy craving, are as though filled with vomit and filth, which are nothing but waste products. The person has extracted from the food all the good and holy elements and left them behind, and all that remains for him is the waste product, and that is what he eats.
There are two ways to explain "beli makom", without space. Simply understood, it means that no spot on the table remained free of the filth. And by way of derash, the Holy One, blessed is He, is called "HaMakom", the Place, who is found everywhere, the place within which the world exists, and therefore "beli makom" means that there is no trace and no place for the Holy One, blessed is He, at that table. For this reason the whole thing is considered waste, and "vomit and filth" serve as a code phrase for idolatry, or for things that no longer have any spiritual root connected to them.
The Table of the Omnipresent:
By contrast, "aval sheloshah she'achlu al shulchan echad ve'amru alav divrei Torah, ke'ilu achlu mishulchano shel Makom baruch Hu" - but three who ate at one table and spoke words of Torah at it, it is as though they ate from the table of the Omnipresent, blessed is He. There is a concept of the "high table," the table of the Holy One, blessed is He, upon which His offerings are placed, and when a person eats from Hashem's offerings he is like one eating at His table. This is the idea the Mishnah is pointing to.
What is the threshold for "words of Torah"?
The Bartenura sets a very low bar, and this is reflected in halachah as well: after the fact, saying Bircas HaMazon is enough. Others are not comfortable with this at all, since Bircas HaMazon is a separate, basic obligation of gratitude, and it does not constitute words of Torah in its own right; we are simply thanking Hashem for the food we received. And if a person does not recite it at all, that is merely a failure to fulfill a Torah obligation, the lowest possible level. It would seem, then, that the Mishnah is speaking of a higher level, that beyond Bircas HaMazon there should be words of Torah at the table. The Shelah brings that even reciting a chapter of Tehillim or something similar is enough to fulfill the requirement, and from here comes the custom of saying passages of Torah and psalms before Bircas HaMazon, in order to make sure that technically words of Torah were said at the table.
But the spirit of the Mishnah is that the three should engage with one another in something that opens the eyes, and not suffice with reciting some verse or other in order to discharge the obligation before Bircas HaMazon.
The verse in Yechezkel:
The Mishnah cites as its source the verse "vayedaber elai zeh hashulchan asher lifnei Hashem" - and he said to me: this is the table that is before Hashem. In context, the prophet Yechezkel sees a vision of the third Beis HaMikdash and describes it, and among other things he describes an altar: "The altar was of wood, three amos high and two amos long, and it had its corners, and its length and its walls were of wood" - the details of the measurements and the materials. And immediately afterward: "and he said to me," the angel said to me, "this is the table that is before Hashem." So what was first called an altar is now called a table.
Three explanations are given of how the verse teaches this:
The Bartenura's explanation: The altar mentioned here, though it is called an altar, refers to the table in the Sanctuary. And between the two descriptions, "altar" and "table," stand the details of the measurements and the materials, and that is Torah. So we have the equation: altar and table are interchangeable when there is a bridge of Torah between them. A table that has Torah upon it becomes like an altar.
A more direct explanation: Since the verse calls the very same thing both an altar and a table, even though it means an altar and not an actual table, we learn from here that a table can be like an altar when it is used properly.
A third, more technical explanation: The verse uses the phrase "shalosh amos." An "amah" is a measure of distance, but without vowels it can be read "imos," as in the expression "yesh eim lamikra ve'yesh eim lamesorah," and this hints at the three main branches of Torah: Torah, Nevi'im and Kesuvim. And when one of these is present at the table, the table is elevated to be like an altar.
In summary: The value of studying this Mishnah is twofold. First, when three people gather together they bear a special responsibility as a group to do something special, and the opportunity should not be wasted. Second, the experience of eating should be an uplifting one, and should include words of Torah, speaking about the Holy One, blessed is He, about His Torah and His concerns, so that the entire meal is elevated. For a person does not eat for the sake of eating itself, but in order to receive strength for the service of Hashem.