The prohibition against breaking the bones of the Pesach (Passover) sacrifice includes two seemingly small words that carry enormous legal weight: "in it." The Mekhilta zeroes in on this phrase to establish a crucial boundary. The ban on breaking bones applies to the Passover lamb — and to the Passover lamb alone. It does not extend to any other offering brought in the Temple.
Without the limiting phrase "in it," the rabbis explain, a logical argument would have extended the prohibition to all sacrifices. The reasoning would run like this: if the Pesach, which is a sacrifice of lesser stringency, prohibits bone-breaking, then surely offerings of greater stringency — such as the daily tamid offering or the festival burnt offerings — should carry the same prohibition. The lighter case restricts; how much more so the heavier case?
The Torah preempts this logic by writing "in it." These two words shut down the kal va-chomer (a fortiori argument) before it can begin. The bone-breaking prohibition is unique to the Pesach. Bones of other sacrifices may be broken, marrow may be extracted, and no violation occurs.
This teaches something important about how the rabbis understood biblical law. Not every rule generalizes. Some commandments are specific to a single context, and the Torah signals this through precise language. The words "in it" are not filler — they are a legal firewall, preventing a rule designed for one sacred occasion from being applied where it does not belong.