Horayot, Chapter Three, Mishnah Five
In the previous mishnah we learned that both acting high priests and former high priests do not rend their clothes when a relative dies. Our mishnah clarifies that halakhah and teaches that the high priest does rend his clothes but not in the same way that an ordinary priest does. In section two, the mishnah makes a further comparison between an ordinary and a high priest.
I) A high priest rends [his clothes] from below and an ordinary priest from above.
II) A high priest offers sacrifices while an onen but does not eat them and an ordinary priest neither offers sacrifices nor eats them.
Section one: If one of the high priests seven close relatives (father, mother, brother, sister, son, daughter or wife) for whom he is obligated to mourn dies, he rends his clothes at the bottom. When Leviticus 21:10 states that the high priest shall not rend his clothes, the interpretation of the rabbis is that he should not rend them in a normal fashion, which is above. In contrast, an ordinary priest rends his clothes the same way that all people do, above.
Section two: An onen is one who has had one of his seven close relatives die, but has not yet buried them (after the burial a person is an avel, a mourner). According to the Torah he is an onen only for the day of the death, but the rabbis extended the status of aninut (being an onen) to include the night after the death, and the entire period until burial. Our mishnah teaches that a high priest continues to offer sacrifices even while he is an onen, as it says in Leviticus 21:12, He shall not go outside the sanctuary. He stays in the sanctuary in order to offer sacrifices. However, he does not eat sacrifices on that day. We learn this from Aarons words on the day that his sons, Nadav and Avihu, die, Had I eaten sin offering today would the Lord have approved? (Leviticus 10:19). It is clear from here that Aaron did not eat sacrifices on that day.
In contrast, an ordinary priest who is an onen may neither offer sacrifices, nor eat them. Since an ordinary priest is allowed to become impure for one of these seven relatives, his status during this period is basically the same as that of ordinary people.