The verse says that Aaron and all the elders of Israel came to eat bread with Moses' father-in-law "before God." But the Mekhilta raises an obvious question: where was Moses himself during this meal? If Aaron and the elders were eating with Yithro, what was Moses doing?
After all, when Yithro first arrived, Moses had gone out to greet him personally — as the verse states, "Moses went out to his father-in-law." So Moses was clearly present. He had welcomed Yithro, told him the story of the exodus, and witnessed Yithro's offerings. Why, then, does the meal scene mention only Aaron and the elders as the ones eating?
The answer reveals something remarkable about Moses' character. He was not eating because he was serving. Moses stood and waited upon the guests, attending to their needs while they sat and ate before God. The greatest prophet in Israel's history, the man who had spoken to God face to face and split the Red Sea, was acting as a waiter at his father-in-law's table.
And where did Moses learn this behavior? From Abraham. When the three angels visited Abraham at the oaks of Mamre (Genesis 18:8), Abraham did not sit with his guests. He stood over them while they ate, serving them personally. Moses followed his ancestor's example. True greatness, the Mekhilta teaches, is expressed not in being served but in serving others.