Rebbi — Rabbi Yehudah HaNasi — offered an alternative reading of (Deuteronomy 16:2): "And you shall slaughter the Passover to your God — sheep and cattle." Rather than identifying the "cattle" with the chagigah offering specifically, Rebbi argued that the verse speaks of any offering that can come from either sheep or cattle. This points to the shelamim — peace-offerings.
From this interpretation, the rabbis derived an important practical ruling: when someone sets aside money for a Passover lamb and has leftover funds after purchasing it, the surplus is used to buy peace-offerings. The money does not simply return to the owner's pocket. It retains its sacred purpose and flows into the next most appropriate category of sacrifice.
This ruling addressed a common real-world scenario. A person might designate a Passover lamb, then lose it, purchase a replacement, and later find the original. Now there are two lambs but only one is needed. What happens to the surplus? Rebbi's teaching provided the answer: the extra becomes a peace-offering.
The underlying principle is that sanctity, once attached to an object or sum of money, does not simply evaporate. It must be redirected. The rabbis treated the holiness of a designated Passover offering as a persistent force that required proper channeling. You could not casually walk away from a sacred commitment — even an accidental surplus had to find its way to the altar.