The Mekhilta notices something peculiar about how the Torah identifies Yithro. In the beginning of the story, Moses is the one who boasts about the relationship. When Moses returns to Midian, the Torah says: "And Moses went and returned to Yether, his father-in-law" (Exodus 4:18). Moses prided himself in being Yithro's son-in-law. The connection gave him status. Yithro was a prominent man in Midian — a priest or an officer, depending on which rabbi you ask — and Moses was glad to claim the association.
But later in the story, the dynamic reverses. By the time Yithro arrives at the Israelite camp in the wilderness, Moses has become the most famous man in the ancient world. He has confronted Pharaoh, brought ten plagues upon Egypt, split the Red Sea, and received the Torah at Sinai. Now it is Yithro who claims the connection.
When people asked Yithro who he was, his answer was simple: "I am Moses' father-in-law." The man who had once been the distinguished one — the one whose name gave Moses credibility — now introduced himself entirely through Moses' fame.
The Mekhilta reads this reversal as embedded in the Torah's own language. The shift from "Moses went to his father-in-law" to "the father-in-law of Moses" tracks a transfer of prestige. It is a story about how the Exodus changed every relationship it touched — even the private one between a man and his wife's father. Before Sinai, Moses needed Yithro's name. After Sinai, Yithro needed his.