The Mekhilta catches a redundancy in the Torah's Passover instructions that most readers would never notice — and from that redundancy, it extracts a legal ruling about where God's protection extends on the most dangerous night in Egyptian history.
The Torah first says the blood should go on "the lintel of the houses where they shall eat it" (Exodus 12:7). Houses of eating. Then, six verses later, it says the blood will be a sign "on the houses where you are" (Exodus 12:13). Houses where you are. If the first verse already established that blood goes on houses, why does the second verse repeat the instruction?
The Mekhilta's answer hinges on the difference between eating and being. The first verse limits the blood to houses where the Passover meal is consumed. But Israelite households in ancient Egypt were not single-room dwellings. Families might eat in one structure and sleep in another. They might have separate buildings for different purposes. If the blood only covered the houses of eating, every other structure was exposed.
The second verse eliminates this vulnerability. "The houses where you are" — in any event, in any capacity, for any reason. Sleeping, resting, storing supplies, sheltering children — wherever an Israelite was physically present, that house required blood and received protection. The phrase "in any event" is the Mekhilta's characteristic way of expressing universality. No exceptions, no conditions, no gaps in coverage.
God's protection on Passover night was not a narrow shield over the dinner table. It was a blanket over every space an Israelite occupied. The blood followed the people, not the meal.