Various levels of atonement coincide with different transgressions. “One size fits all” does not fit all in reference to penance, because sins occur on various levels. Two people might commit the same act of infraction; yet, their modes of atonement are different. Although, on the surface, their sins may appear similar, Hashem gazes into the hearts and minds of the sinners and distinguishes between them.
Aharon was commanded to bring a calf as a Korban Chatas, sin-offering, to let him know that, with this calf, Hashem would grant him atonement for his actions in creating the Golden Calf (Rashi). Klal Yisrael also brought a calf as a korban to atone for its role in building the Golden Calf. This calf, however, was not a sin-offering, but rather, a Korban Olah/burnt/elevation offering. Why was there a distinction between the two offerings? Klal Yisrael brought an olah, while Aharon’s calf served as a chatas.
Horav Yisrael Belsky, zl, observes that a Korban Chatas atones for a maaseh aveirah, sinful act, commission of the sin. One who has erroneously committed an aveirah which, if carried out with aforethought would be punishable by kareis, Heavenly excision, brings a chatas. On the other hand, the Korban Olah is brought for improper thoughts, or plans one has for committing a sin, but does not actually execute. In other words, the olah atones for sins of the mind, while the chatas atones for sins of commission.
Aharon HaKohen’s sin was different than the one committed by the people. Klal Yisrael’s part in the chet ha’eigel, Golden Calf, was primarily a sin which involved sinful thinking. They were concerned that Moshe had not returned. They felt a replacement was in order, but they worried that the replacement could not do everything that Moshe Rabbeinu did. This is where the people were divided. Those who felt that the idol had powers were idol worshippers and, consequently, they died at the hands of the sword wielded by the Leviim. The rest of the people did not worship the idols; thus, they were only guilty of sinful thoughts. Their proper atonement was a Korban Olah which atones for sins of the mind.
Aharon, on the other hand, never harbored any thoughts concerning the validity of the idol’s godliness. It was a molten image which he had fashioned in order to satisfy the clamoring of those who sought an idol to replace Moshe. Aharon knew that it was impossible to replace Moshe. This idol was a spoof. Nonetheless, he made it and, as a result, he required atonement. Veritably, it resolved the immediate crisis, but it destroyed the spiritual standing of Klal Yisrael. An inappropriate action which did not reflect sinful thought still required atonement. Thus, Aharon brought a chatas for his participation in creating the eigel.