Mishnah Shevuot 2-3

Until now, we’ve been talking about a person who became tameh (ritually impure) and then entered the Beit HaMikdash. This Mishnah discusses somebody who entered the Beit HaMikdash pure, but then became tameh while he was inside. The Mishnah says that if someone became tameh while he was already in the courtyard of the Beit HaMikdash, and at that point realized he was tameh, but then for whatever reason forgot that he was tameh while still knowing that he was in the Beit HaMikdash—or the opposite, he didn’t remember that he was in the Beit HaMikdash but did remember that he was tameh—or if he forgot both, that he was tameh and that he was in the Beit HaMikdash, and while in that state of not realizing, he bowed down to Hashem. We’re talking about a full bow: face down on the ground, arms extended outward. It takes a few seconds to get into that position. If he stayed around long enough to bow but didn’t actually bow, or if he left by taking the long route out of the Beit HaMikdash, in all of these cases he is obligated to bring a korban chatat (sin offering) for this sin. He basically stayed when he was supposed to leave right away. The halakha (Jewish law) is that somebody who becomes tameh while in the Beit HaMikdash has to leave as quickly as physically possible. This person waited and bowed to Hashem, waited around as long as a bow would have taken, or took the long way out of the Beit HaMikdash. He didn’t leave right away, and therefore he is obligated to bring a korban (offering) for this sin. But if he exited by the short route, without bowing or delaying whatsoever, then he would be patur, he would not be obligated to bring that korban. There’s a halakha that if the Sanhedrin made a mistake in halakha and allowed something that was really forbidden, and it was punishable by karet (spiritual excision), then the Sanhedrin has to bring a special chatat offering if the majority of the Jewish people followed their ruling, transgressed, and made a mistake. They followed that problematic ruling. This offering that they have to bring is called a par he'elem davar shel tzibbur. They have to bring a bull; that was a matter hidden from the community, a mistake made on a community level, sanctioned by the Beit Din (rabbinical court). The Mishnah in Horayot comments on that and says that the Sanhedrin is not obligated to bring this korban if they gave a ruling on a positive commandment—that means an action-based commandment—that has to do with the Beit HaMikdash. But it doesn’t tell us which mitzvah (positive commandment) specifically it is talking about. So the Mishnah here will explain. The halakha that requires a person to leave the Beit HaMikdash right away if he becomes tameh is the mitzvah, the positive commandment concerning the Beit HaMikdash, that we mentioned in Horayot. If the Sanhedrin makes a mistake in ruling that a person who became tameh in the Beit HaMikdash does not have to leave right away by the shortest route, when really he is obligated to leave right away, then they would not be obligated to bring the special korban chatat to atone for their mistake. Even if a majority of the Jewish people followed their ruling, they don’t have to bring it in this case; it’s the one exception to the law.