Keritot, Chapter Two, Mishnah One
Generally a person who is impure and then immerses in a mikveh can begin to eat sacrifices after immersion. However, there are four categories of people who must first bring sacrifices before they can eat other sacrifices. This process is called a ceremony of atonement.
Our mishnah also mentions another category, but since tomorrows mishnah discusses it more fully, we shall explain it tomorrow.
1) There are four persons who require a ceremony of atonement, and there are four who bring a sacrifice for willful as well as for inadvertent transgression.
2) The following are those who require a ceremony of atonement: the zav, the zavah, the woman who gave birth and the metzora.
3) Rabbi Eliezer ben Jacob said: also a convert is regarded as a person who still requires a ceremony of atonement until the blood has been sprinkled for him; the same applies to the nazirite with reference to wine, haircutting and uncleanness.
Section one: This section introduces todays and tomorrows mishnah.
Section two: A zav is a man who has an abnormal genital discharge (see Leviticus 15:15) and a zavah is a woman with an abnormal genital discharge (see Leviticus 15:29-30). Both must bring sacrifices before they complete their purification process. So must a woman who gave birth (as we learned in 1:3) and a person who had some type of skin disease (Leviticus 14:10ff).
Section three: Rabbi Eliezer ben Jacob adds two more to this list. A convert who has already been circumcised (if he is a man, of course) and immersed in the mikveh, must bring a sacrifice. He cannot eat sacrifices until the blood from the olah that he brings is sprinkled on the altar. Similarly, a nazirite cannot drink wine, cut his hair or become impure from contact with a dead body until he brings his sacrifices (see Numbers 6:14 and Mishnah Nazir 6:9). Both of these are also cases where a person needs to bring a sacrifice to complete the process of purification.