As we learned on yesterday’s daf the second perek of Massekhet Zevaḥim deals with situations where there is some problem with the person who brings the sacrifice. One of the examples that appears in the Mishna is the case of an onen who sacrifices. An onen is someone who has a close relative who has passed away, but has not yet been buried. Generally speaking, Jewish law anticipates that such a person is supposed to focus entirely on tending to the deceased and is free of all other mitzvot.
A number of reasons are suggested by the Gemara as possible sources for the law forbidding an onen from carrying out the sacrificial service.
The first suggestion is that we learn it from the passage about a kohen gadol who is commanded to continue his service in the Temple even after a close relative has died (see 21:12). According to that pasuk, which says lo yetze ve’lo yeḥalel, the kohen gadol cannot leave the Temple, and that in doing so his service will not become meḥulal – made mundane. The implication, as understood by the Gemara, is that this is a unique law pertaining to the kohen gadol, but if any ordinary kohen in that situation were to remain in the Temple, his service would become meḥulal.
Both Rashi and the Rambam in his Sefer HaMitzvot (principle number 5) understand from the Gemara that the term ve’lo yeḥalel is not a prohibition for the High Priest to make his service mundane by leaving the Temple, rather it is an explanation of why he is required to remain at his post – his service will not be affected by his status as an onen, even though the status of other kohanim would be affected. The Ramban disagrees with this approach, noting that many of the Ge’onim do seem to count ve’lo yeḥalel as a prohibition forbidding the High Priest from leaving the Temple when he is an onen. He suggests that the Gemara should be understood as saying that there is a unique law forbidding the kohen gadol from leaving the Temple when he is an onen, since were he to leave, it would render his service mundane. The service of ordinary priests, however, would not be meḥulal were they to leave the Temple – since were their service acceptable the Torah would not permit them to leave.