The concept behind the mitzvah of birchat hamazon, Grace after Meals is one that is easy to understand.  After eating food that God has given us, the Torah commands to thank and praise the One who gave us this food. The preliminary tefila called birchat hazimun is of Rabbinic origin. The word zimun means to invite or prepare. Our Rabbis established that when three or more people eat together they should join together to recite Birchat Hamazon, one person leads, he invites and prepares the others to bless God. This birchat hazimun changes when there are ten men present. What is the meaning behind this birchat hazimun and its change?
    Birchat hazimun consists of a responsive recitation between the leader and the rest of the zimun, the people who ate. The leader begins by calling all present to bless and the zimun answers with the pasuk of yehi shem Hashem mivorach…, which translates as “Blessed be the Name of Hashem from this time and forever.” The leader then asks permission and instructs the group to bless the Provider of food. The zimun then blesses God, “of Whose food they ate” and the leader repeats after them. In essence the birchat hazimun is joining all present together to recite birchat hamazon as one. Our Rabbis teach us that when many do a mitzvah as one, their merit is much greater than a mitzvah performed individually. Indeed, each member of the group will reach a level far higher than if they had acted alone.
    In Judaism, we recognize that the mitzvot are a precious gift given to us by God, in order to enable us to receive eternal reward in the World to Come. Just as when a person receives a gift he thanks the goodhearted person who gave it, so too a Jew thanks his Benefactor for the gift of mitzvot. Therefore it follows that almost every mitzvah that we do has a bracha that precedes it, in which we praise God for giving us the opportunity to serve Him in this way. This is also true of the mitzvah of Birchat Hamazon, we bless God for giving us the mitzvah of thanking Him for our food and that blessing is the birchat hazimun.
    It is interesting to note that the opening words of rabotai nevarech and the pasuk of yehi shem are not mentioned in the Gemara. The Aruch Hashulchan suggests that these were added as an introduction in order for people to be able to prepare themselves for the mitzvah. He quotes the Zohar who says that any holy act or mitzvah needs emotional preparation before performing it. This concept is similar to the hineni muchan u’mezuman that many recite before certain mitzvot. In comparison, the words of nevarch sh’ achalnu mi’shelo are traced back to Avraham Avinu. When Avraham used to serve his guests they would of course thank him. Avraham in turn would tell them not to thank him, but rather to thank God, of Whose food they had eaten.
    Although, as mentioned, birchat hazimun is a bracha, it is not a conventional one. Each bracha follows the conventional format having shem, the name of Hashem and malchut, mention of God’s kingship. Birchat hazimun does not mention God’s name nor does it speak about His kingship. The Aruch Hashulchan explains that because birchat hazimun is a bracha that is said to introduce many brachot that all have shem and malchut, it itself does not need to make mention of them. Additionally, it is a bracha that is not said all the time—only with three or more.
    As we mentioned above, when there is a minyan present, we add the name of God to our zimun. The Aruch Hashulchan tells us that this is based on a pasuk from Tehillim that says, “…in congregations they bless God.” This is taken to mean that we may only mention the name of God in group prayer when there is a “congregation.” We know from other sources in the Torah that a congregation is no fewer than ten.
    May our newfound understanding of this bracha lead us to a greater fulfillment of the mitzvah of birchat hamazon that it introduces.