One who was contaminated or was on a distant journey, and had not observed the First [Pesach], must observe the Second. [If] he erred or was prevented, and [therefore] did not observe the First [Pesach], he must observe the Second. If so, why is it said: One who was contaminated or was on a distant journey (Numbers 9:10)? Because these are exempt from kares, but those are liable to kares.