Rashi on Leviticus 6:19/רש"י על ויקרא ו׳:י״ט

1המחטא אתה means the priest who performs those rites connected with it (i. e. those connected with the sprinkling of the blood), he is called the מחטא because it is through him that it becomes a sin-offering.

2המחטא אתה יאכלנה THE PRIEST THAT OFFERETH IT MAY EAT IT — i. e., the priest who is fitted to carry out the rite (so that the words denote: Any priest who may offer it as a sin-offering may eat of it; they do not refer to that priest alone who offered it). Thus there is excluded a priest who is unclean (and therefore unfitted) when the blood is sprinkled — that he has no share in the flesh. One cannot say that Scripture here forbids the eating of it to ANY priests (i. e. even to clean priests) except him who sprinkles the blood, because, you see, it is stated later on (v. 22), “All the males among the priests may eat thereof” (cf. Zevachim 99a).