We are opening the twelfth chapter of Tractate Zevachim, and beginning with Mishnah 1. The question that the Mishnah comes to answer is: Which kohanim are entitled to receive the meat of the korbanos that were offered on that day? In almost all korbanos there is a portion given to the kohanim, and therefore we must clarify who is entitled to the meat. Let us begin with some background information.
The division of the kohanim into mishmaros and batei av:
Mishmar: Since the days of Shmuel the Prophet and King David, the kohanim were divided into twenty-four groups, and each group is called a mishmar. The mishmar served from Shabbos to Shabbos, once every twenty-four weeks. On Yom Tov and the festivals, all of them came, of course, and this was a busy period when all hands were needed; but during the rest of the year, each mishmar served only two weeks out of the year.
Beis av: Even within the mishmar itself, there is a division into seven subgroups called batei av, and each beis av served on one day of the seven days of the week.
It turns out, therefore, that a kohen performs the service of the Temple - ignoring the festivals when all the kohanim are in Jerusalem - exactly two days a year. The kohanim who perform the service on that day, the members of the serving beis av, are the ones who will receive the meat as well as the hides of the animals brought on that day.
The question in our Mishnah is who is entitled to receive the meat among the members of the beis av. The fundamental principle, the details of which will be explained later in the Mishnah, is that whoever was fit to serve and perform the service in the Temple - is the one entitled, and whoever was not fit for it - is not entitled.
Tevul yom and mechusar kippurim:
Two additional basic concepts are needed to understand the opening of the Mishnah. A tamei person is forbidden by rabbinic law to enter the Temple, and certainly a tamei kohen cannot perform the service - and his service is invalid. The typical way to remove tumah is immersion in a mikvah, but a remnant of tumah remains upon the person even after he emerges from the mikvah. This person is called a tevul yom, and he remains tamei for the remainder of that day.
Thus a kohen, and even someone who is not a kohen, who touched a dead mouse or sat on the same chair that a niddah or zav sat upon and the like - becomes tamei. He will immerse in a mikvah, and for the remainder of the day he will be called a tevul yom. The remnant of tumah that remains in him has the status of a sheni l'tumah, which means that after he emerges from the mikvah he is permitted to do certain things - such as eat maaser sheni - but he cannot eat Terumah, and certainly he cannot eat kodashim.
Once nightfall (erev shemesh) arrives - and this is the subject of the very first Mishnah on the first page of the entire Shas, at the beginning of Tractate Berachos - meaning at tzeis hakochavim, when three stars emerge, the person becomes completely tahor, and the remainder of his tumah as a tevul yom disappears. From this point on, with the fall of night, he is permitted to eat kodashim.
For example: A Yisrael who wishes to participate in eating the korban pesach, and became tamei on the fourteenth of Nissan because he touched a dead mouse or the like - he will immerse in a mikvah, and for the entire rest of the day his status is that of someone who is tamei, but when night comes he is permitted to participate in the Pesach seder, since he has become tahor and is no longer a tevul yom after three stars have emerged.
However, there are certain types of tamei individuals who, even after they have immersed in a mikvah and even after nightfall and the emergence of three stars - a remnant of tumah remains in them, and they are called a mechusar kippurim, meaning they lack atonement: they still need to bring a korban. In our Mishnah, in the context of a kohen, we are dealing with two possibilities: a zav who saw three emissions, who has korbanos, or a metzora. The zav and the metzora become tamei for a period of seven days, and at the end of the seven days they have different procedures, but in both cases they are able to immerse in a mikvah to become tahor.
For the remainder of the day they remain a tevul yom, and at nightfall they descend from the level of a tevul yom, which is like a sheni l'tumah, to the level of a mechusar kippurim, which is like a shlishi l'tumah - meaning a remnant of tumah still remains in them. At this stage he is permitted to eat Terumah, but he cannot enter the Temple and he cannot eat kodashim. He must wait for the next day and bring his korbanos - the korbanos of the metzora or the korbanos of the zav, each according to his law - and only after that is he atoned for and becomes completely tahor, and from that point he can enter the Temple and eat kodashim.
The language of the Mishnah:
"Tevul yom" - A kohen who immersed in a mikvah that same day, and therefore cannot perform the service in the Beis Hamikdash for the rest of the day, even if his family group is serving today, since a trace of tumah remains upon him.
"Umechusar kippurim" - And even a kohen who immersed in a mikvah yesterday and had the sun set upon him, but still has not brought his offerings, and therefore a trace of tumah remains upon him and he cannot perform the service.
In both of these cases the Mishnah rules: "Einam cholkin bekodashim leechol laerev" - They do not share in the distribution of the kodashim, and they do not get to eat from the meat that night. Even for a tevul yom, who upon nightfall becomes as pure as all his peers, this does not help: At the time the kodashim were offered during the day he was not fit, and therefore he does not participate in eating the meat.
An onen:
An onen is someone who has lost one of his seven close relatives: his father, mother, sister, brother, son, daughter or wife. On the day the relative dies, the onen is in deep mourning, and the Torah forbids him, among other things, from eating kodashim. His service in the Beis Hamikdash is also invalid.
The Mishnah states: "Nogea ve'eino makriv, ve'eino cholek leechol laerev" - He is permitted to touch kodashim, since he is not tameh; but he cannot participate in offering the sacrifices, because he is disqualified; and that night he will not receive any of the meat and is not permitted to participate in eating it, since he was not fit to serve during the day. That exact same principle applies here too.
With the word "nogea", the Mishnah alludes to something that is not explicitly stated in it: There is a rabbinic law that an onen is not permitted to eat from the kodashim until he immerses in a mikvah again. Even if he immersed previously, and afterwards became an onen for the rest of the day and sat on the steps of the mikvah crying bitterly until it was time to eat - he must nevertheless immerse one more time before eating from the kodashim. The reason for this: Since he cannot perform the service and is distracted as an onen, he might not pay attention to matters of taharah and become tameh. Regardless, if he did not immerse again and touched kodashim - his touch does not make them tameh, and this is what the Mishnah teaches with the word "nogea".
Baalei mumin:
What is the law regarding kohanim who cannot perform the service because of a blemish that disqualifies them from serving?
"Bein baalei mumin kavua" - A permanent blemish that will never pass, such as if he is missing a finger or a leg, with which he is always disqualified.
"Bein baalei mumin over" - A temporary blemish, such as if his hair will grow back, and after he heals he will be able to serve again.
In both of these cases the law is "Cholkin ve'ochlin aval lo makrivin" - Even though they cannot perform the service, they are permitted to take a share and eat from the meat, but they cannot actually offer the sacrifices. They can do other things, and there are many matters around the Beis Hamikdash that a blemished kohen participates in, but the sacrificial service itself they cannot do.
The principles arising from the Mishnah:
"Vechol she'eino ra'ui la'avodah, eino cholek babasar" - Anyone who is unfit to perform the service, such as one who was tamei or an onen and the like, does not receive a share from the meat of that day's service, even if the problem passed by nightfall. Blemished kohanim are the exception to this rule.
"Vechol she'ein lo babasar, ein lo ba'orot" - One who is not entitled to receive from the meat is also not entitled to a share in the hides. We must remember that when bringing a sacrifice, such as an olah, the animal has a hide, and the hides are valuable. But one who is not entitled to the meat, because he was tamei on that day, also does not receive a share in the hides of the animals from that day.
"Afilu tamei bish'at zerikat damim vetahor bish'at hektar chalavim" - Here we are not speaking about an olah, since the discussion is about eating the meat, but rather a chatat or an asham and the like. The burning of the emurim of the chatat and the asham can be done all night, and therefore it is possible that at the time the fats were burned on the altar, hours later, the kohen was completely tahor, since he was only a tevul yom. Nevertheless, "eino cholek babasar": he does not merit to participate in eating the meat, because according to the verse, one who was not fit for the service of the blood at the time it was performed cannot participate in the meat even afterward.
And this is the verse that the Mishnah brings: "Shene'emar: hamakriv et dam hashlamim ve'et hachelev mibnei Aharon, lo tihyeh shok hayamin lemanah" - The one who actually offers the blood of the shelamim and the fat, which are the emurim, and he is from the sons of Aharon the kohanim, is the one entitled to receive the right thigh, the right hind leg, which is one of the gifts given to the kohen from the shelamim along with the breast. We find that one who is not entitled to perform the service of the blood is also not entitled to a portion of the meat.
In summary: In this Mishnah, we learned that the kohanim are divided into twenty-four watches and into seven households (batei av) in each watch, and the members of the household serving on that day are the ones entitled to the meat and the hides. We discussed the laws of a tevul yom and a mechusar kippurim and the remnant of tumah that remains in them, and we learned that even if they become tahor by nightfall, they do not share in the kodashim, and the same applies to an onen, who may touch but does not offer and does not share. We also saw that blemished kohanim, whether with a permanent or temporary blemish, share and eat but do not offer, and that the rule is that anyone who is unfit for service does not share in the meat, and anyone who does not share in the meat does not share in the hides, as derived from the verse "He among the sons of Aharon who offers the blood of the shelamim and the fat, to him shall the right thigh be for a portion."