Kerisos, Chapter 2, Mishnah 1. Our Mishnah presents the framework for the entire chapter: scenarios where a person brings a sacrifice that deviates from the standard rules. Two rules are the focus of the chapter.
The first rule - a Chatas comes to atone for a sin: There are four sacrifices that are defined as a Chatas (a Chatas sacrifice is their "recipe"), and nevertheless they do not come to atone for a sin committed by the one who brings them. We have already seen two of them.
The second rule - a sacrifice is only brought for unintentional sins: A person does not bring a sacrifice for atonement unless he acted unintentionally, without intent to transgress the Torah, and this applies to all Chatas sacrifices. One who transgresses intentionally, with forethought, is not given the right and opportunity to bring a sacrifice; he must stand before Hashem, repent, face the consequences of his actions, and reconcile with his Creator, and he has no "magic wand" of a sacrifice to achieve atonement. However, there are four exceptions, where even one who transgresses intentionally and willfully must bring a sacrifice - and these are not Chatas sacrifices but Asham sacrifices. This is the subject of the chapter.
The structure of the Mishnah:
"Arba'ah mechusrei kippurim" - four cases where the person did not sin at all, and nevertheless he brings a Chatas to complete his purification process. Until he brings his sacrifices, a trace of tumah remains upon him, and because of it he cannot eat consecrated foods and cannot enter the Temple, and he is like a third degree of tumah. This concluding sacrifice is what makes him completely pure.
"Ve'arba'ah mevi'in al hazeidon keshagagah" - four transgressions for which a person brings a sacrifice even though he acted intentionally: he knew the act was forbidden and did it anyway, and nevertheless he brings a sacrifice. In the following Mishnayos, we will deal with these cases.
Mishnah 1 deals with the first group: "Eilu hen mechusrei kippurim: hazav, vehazavah, vehayoledes, vehametzora" - these are those lacking atonement: the zav, the zavah, the yoledes, and the metzora.
The zav: A man who has a mysterious discharge from his organ, and it is not seminal fluid (its nature is unknown - it might be pus or another liquid). He must track the sightings: if he saw a second time within two days, he becomes a zav and is impure for seven days, but does not require sacrifices. If he saw three separate sightings within three days, he is a full zav, and requires seven days without further discharges, at the end of which he immerses in a mikvah and brings sacrifices: a pair of birds.
The zavah: A woman who sees blood outside of her regular menstrual cycle, meaning between the eighth and eighteenth days, for three consecutive days. Unlike the zav: if she saw on the first day but not on the second day, she begins counting anew, whereas a zav who saw twice on the first day, did not see on the second day, and saw on the third day, becomes a full zav. The zavah is impure, and must wait seven clean days, immerse in a mikvah, and bring a pair of birds.
The yoledes: A woman who gives birth to a child or miscarries, as was explained above.
The metzora: Someone diagnosed as a metzora, man or woman, who has a skin affliction. He must wait until his affliction heals, and once he has recovered, he is permitted at a certain stage to undergo a purification process that includes immersion in a mikvah and bringing sacrifices (and we will expand on all of this later). Until he brings his sacrifices, he is lacking atonement, and he has no atonement and cannot enter the Temple itself.
The meaning of the terms 'zav' and 'zavah' is flowing, as in the verse "eretz zavas chalav udevash" - a land flowing with milk and honey. Both experience a mysterious flow exiting their bodies, and this is the common denominator between them, in its beginning and its end.
The opinion of Rabbi Eliezer ben Yaakov - six who lack atonement:
"Rabbi Eliezer ben Yaakov omer: ger mechusar kaparah" - a gentile who wishes to convert to Judaism while the Temple stands is required to undergo three necessary steps: circumcision, immersion in a mikvah, and bringing a sacrifice. According to Rabbi Eliezer ben Yaakov, "ad sheyizarek alav hadam" - until the blood of his sacrifice is sprinkled on the altar, he is forbidden to enter the Temple and eat consecrated foods, and he is truly lacking atonement. This is how he understands the essence of the convert.
It appears that the Tanna Kamma disagrees with this, and there are two approaches in explaining his opinion: First, that bringing the sacrifice is what permits him to marry a Jewish woman. Second, that although he does not eat consecrated foods until he offers his sacrifice and the blood is sprinkled on the altar, this is not because he is considered impure, but rather because he is not yet Jewish - and this is what prevents him. Therefore, he is not called one who lacks atonement according to the Tanna Kamma.
For our purposes, it must be clarified that the term "sprinkled" is not meant exclusively: the convert can bring a male sheep as a burnt offering, and he can bring birds - and with birds there is no sprinkling, only squeezing out the blood, but it is all the same. The point is that the blood of the sacrifice reaches the altar.
The second one that Rabbi Eliezer ben Yaakov adds is "hanazir" - someone who accepted upon himself to refrain for a certain period of time from consuming grape products, cutting his hair, and contracting ritual impurity from a corpse. At the end of his process, he must bring offerings, and until he brings his offerings, or at least one of them, he is forbidden to resume drinking wine, cutting his hair, or becoming impure from a corpse. Therefore, says Rabbi Eliezer ben Yaakov, he too is considered someone who lacks atonement.
The Tanna Kamma does not hold that such a person is considered to be lacking atonement: there is no issue of tumah and taharah here at all, but rather a completely different matter - the permission to do what was forbidden to the nazir. Therefore, the Tanna Kamma does not include this in the list either.
Halachah: The Rambam explicitly writes that there are four individuals who lack atonement, and he mentions neither the convert nor the nazir - meaning, the halachah does not include these two in the list.
In summary: In this chapter, we will discuss two exceptions to the rules of offerings: four chatas offerings that are not brought for a sin, and four transgressions for which an offering is brought even when committed intentionally. In our Mishnah, the four individuals who lack atonement were listed - the zav, the zavah, the woman after childbirth, and the metzora - whose offerings conclude their purification process and permit them to partake of kodashim and enter the Temple. Rabbi Eliezer ben Yaakov added the convert and the nazir, while the Tanna Kamma holds that their situation does not involve tumah and taharah, and this is how the halachah is ruled by the Rambam.