The Torah in Parashat Sav (beginning of chapter 7) introduces the guidelines for the offering of the Korban Asham (“guilt sacrifices”) which was required to atone for certain misdeeds. The Sefer Ha’hinuch lists the obligation upon the Kohanim to comply with these guidelines as the 140th Biblical command.
The Ramban, commenting to Parashat Vayikra (5:15), discusses the difference between the two different kinds of sin offerings – Hatat and Asham. The Torah makes it clear that these are two separate categories of sacrifices, despite the fact that both are brought to atone for wrongdoing. The Ramban explains that the word “Het” (“sin”) literally means “miss,” as in missing the target when shooting arrows. One is said to commit a “Het” when he makes a mistake, when he “misses” the goal that he was expected to accomplish. And thus the Hatat offering is brought primarily for unintentional sins, for instances where one simply “missed the mark” and did not act as he was supposed to act. The word “Asham,” however, is derived from the word “Shemama,” which refers to desolation and destruction. An Asham is required for situations of more severe wrongs, for which one is deserving of “destruction,” but he is granted the opportunity to atone for his wrongdoing by offering a sacrifice. Indeed, on some occasions, an Asham is offered even for an intentional violation of a Torah command.
A Kohen who fails to follow the procedures outlined by the Torah for offering the Asham sacrifice has transgressed this affirmative command.