ציטירנדיקער פּירוש אויף ישעיהו 28:8

Rabbi Shimon said: if three have eaten at one table and have not spoken there words of Torah, [it is] as if they had eaten sacrifices [offered] to the dead, as it is said, “for all tables are full of filthy vomit, when the All-Present is absent” (Isaiah 28:8). Rabbi Shimon’s first statement is based on a pun on the verse in Isaiah. The literal translation of the verse according to JPS is, “Yea, all the tables are covered with vomit and filth so that no space is lift.” The words “so that no space is lift” can also be interpreted to mean, “when the All-Present is absent” for the word for “All-Present” and “space” are one and the same. Sacrifices to the dead are how Rabbi Shimon interprets the word “filthy vomit”. The reason that he assumes that this is three is that a communal meal must have three. This is also the minimum number that must be gathered in order to do a communal grace after meals “birkat hamazon”.