Rabbi Shimon would say, and they didn't say any words of Torah at that table. It's as if they ate from the offerings of the dead, which means offerings to an idol. When three people are together, they have to issue an invitation to group together as a chabura, as one united group. So if that group is meeting for mundane matters, only for physical pleasures, just to enjoy themselves, then it would not be a sacred meal. But if they uplift their meal with words of Torah, then it's a joint effort involving more than just eating and drinking, but service of Hashem.
And we prove that if they don't do this, it's a problem, and it's as if they're bringing a korban (offering), or they're eating from the korban to the idols, because all the tables are full of vomit and excrement, because they ate without mentioning the name of Hashem. But if three people ate at the same table and did say words of Torah together, it's as if they ate from the table of Hashem. As the pasuk (verse) in Yechezkel says, “Vayedaber elai, zeh hashulchan asher lifnei Adonai,” he said to me words of Torah, and therefore this is the table that is before Hashem.