The Torah uses an unusual word — "michsah" — when describing how the Passover lamb should be allocated. (Exodus 12:4) says the lamb must be divided "according to the michsah of souls." The Mekhilta explains that "michsah" means a count. The lamb must be slaughtered specifically for the people who have been counted and registered for it.
This raises an immediate legal question. What happens if someone slaughters the lamb without this specific intent — without counting particular people? One might think the offering would still be valid, since the physical act of slaughter was performed correctly. But the Torah repeats the requirement: "Each according to his eating shall you count." The repetition signals that intent matters as much as action.
The Mekhilta derives from this repetition that a Passover lamb slaughtered without being designated for specific individuals is not kosher for the Passover offering. The sacrifice is invalidated not by a physical defect but by a mental one — the absence of proper intent.
This teaching reveals a profound principle in Jewish sacrificial law. The physical mechanics of slaughter are necessary but not sufficient. The person performing the act must have the correct people in mind. Sacrifice in Judaism is never merely a mechanical procedure. It requires kavvanah — directed intention. The Passover lamb had to be killed for someone, and that someone had to be identified in advance. Anonymous sacrifice was no sacrifice at all.