Shir Ha-Ma'alot #5

Zimun – Invitation
"Three people who ate [bread] together are required to join in a zimun [the collective invitation to bless together after eating]" (Mishnah Berachot 7:1). What did our Rabbis see in the mitzvah of blessing after eating to establish that it be performed in a partnership? Ha-Rav Shimshon Rafael Hirsch explained that the daily struggle to survive is liable to transform people into enemies, and when a person rules over his fellow it is to the first person’s detriment. Therefore, particularly after people have pleasure from the goodness of this world, it is proper that they unite together to give gratitude to God with love and fraternity without jealousy or rivalry. When they remember that the source of goodness is the Master of the Universe, people will be reminded that all of us have one Father and we will be bound together in friendship (commentary on the siddur). The earliest source of the zimun is our forefather Avraham himself, the island of kindness, who would generously provide from his goodness to anyone who passed by. Our Sages relate that after they ate and drank and were ready to bless him, he would say to them: Did you eat of mine? Thank, praise and bless He who spoke and the world came into being (Sotah 10b).
By the way, the opening of the zimun, "Rabotai nevarech – Gentlemen, let us bless," or similar phrases, do not have their source in the Talmud but in the Zohar, based on the idea that all matters of holiness require invitation, and that anything that involves holiness requires preparation (Zohar, beginning of Devarim). Something involving holiness is not to be done casually, such as people performing commandments by rote (see Yeshayahu 29:13), rather one must prepare one’s soul: Know before whom you stand.