Introduction The first four mishnayot of our chapter deal with what is called “Pesah Sheni”, the second pesah. The laws of Pesah Sheni are taught in Numbers 9:9-13. Pesah Sheni is observed on the fourteenth of Iyyar, one month after the first Pesah.
He who was unclean or on a far-off journey and did not keep the first [Pesah] must keep the second. The Torah specifies that a person who was unclean during the first Pesah, or one who was far from Jerusalem on a long journey and therefore could not offer the first Pesah must observe Pesah Sheni. There is no new information in this section in the Mishnah it is taught in order to serve as an introduction to the following clauses.
If he unwittingly erred or was prevented and did not keep the first, he must keep the second. This section teaches that not only one who was unclean or far away is allowed to keep Pesah Sheni, but also one who couldn’t offer the pesah on its original date for another reason. This would include an error in remembering the date of Pesah or any other thing which prevented him, as long as it was not intentional.
If so, why does it say “an unclean person” and “one who was one a long journey” specified? That these are not liable to karet, whereas these are liable to karet. This question is midrashic in nature it asks a question about a verse in the Torah. If everyone who through no fault of his own cannot observe the first Pesah is allowed to observe Pesah Sheni, then why does the Torah specify these two categories of people? The answer is that someone who was unclean or on a far-off journey for the first Pesah and then did not keep Pesah Sheni is exempt from the punishment of karet, the usual punishment for one who didn’t observe Pesah. This is true even if they intentionally did not keep Pesah Sheni. This is because they were exempt from the first Pesah and the Torah does not mention the punishment of karet with regard to one who does not keep Pesah Sheni. In contrast, a person who didn’t keep the first Pesah because of error or because something prevented him and then he intentionally didn’t observe Pesah Sheni is liable for karet. These people were obligated for the first Pesah and even though something prevented them from doing so, the obligation still stood. The Torah specifies concerning this person, “But if a man who is clean and not on a journey refrains from offering the passover sacrifice, that person shall be cut off from his kin (karet)” (Numbers 9:13). The rabbis say that this verse refers to one who unintentionally missed the first opportunity but intentionally skipped the second.