The tzitz – the priestly crown or headplate – was worn by the kohen gadol – the High Priest – as part of his Temple uniform. According to the Torah (Sefer Shemot 28:38) the tzitz served a specific purpose. By wearing it, “Aaron shall bear the iniquity committed in the holy things, which the children of Israel shall hallow, even in all their holy gifts; and it shall be always upon his forehead, that they may be accepted before the LORD.” This was understood by the Sages to mean thatit atones for ritual defilement that might occur in the Temple.
This idea is brought in the Gemara on today’s daf (=page) by Rav Papa as an explanation of the disagreement in theMishnah. In a situation where part of the Temple service became ritually defiled, e.g. when one of the two loaves brought on Shavu’ot becomes ritually defiled, or one set of the lehem ha-panim – the shew-bread (see above daf 7) becomes impure, can the remaining bread be eaten? Rabbi Yehudah rules that they must all be destroyed, since a communal offering cannot be divided into parts. The Sages of the Mishnah disagree and rule that what has become ritually defiled must be destroyed, but that the rest remains unaffected and can be eaten.
Rav Papa suggests that this difference of opinion is based on how broad the power of the tzitz should be viewed. According to the Sages, the power of the tzitz to atone for ritual defilement in the Temple is such that it works not only on sacrifices that have already been brought so that they are considered valid, but also on things that are to be eaten by thekohanim. Although it cannot purify a ritually defiled offering, it can give it the status of a valid offering to the extent that the sprinkling of the blood of such a sacrifice would be acceptable and the remaining parts of the offering will be considered valid and can be eaten by the kohanim according to their regulations. Rabbi Yehudah limits the power of the tzitz, and since part of the sacrifice has become disqualified the blood cannot be sprinkled and the loaves cannot be eaten.
Ultimately, the Gemara rejects Rav Papa’s explanation, and Rabbi Yohanan concludes that Rabbi Yehudah simply had an longstanding oral tradition that a partial communal offering cannot be brought.