Aaron was completely free of error, except for the incident with the Golden Calf. This error was a heavy burden on his soul. He was concerned that the Creator would reject his sacred work and his priesthood. Moses said to him, “You don’t have to be afraid! The Omnipotent forgives you!” It was only then that Aaron went up to the altar. (M. Weisman, “Midrash Mispar,” Parshat “Shemini”).
Aaron considered himself unworthy of the sacred work and the priesthood because he felt within him the previous breach, the previous crisis, the previous shattering, from the sin of the golden calf.
So, he had to pass through a turning point in order to rise up again. Only then was he ready for the correction of the sins committed at the time of the worship of the golden calf.
He began to feel that the sin of the golden calf was arranged intentionally for his present correction. This means that this problem had to be revealed precisely in this way otherwise it would not have been revealed. Now it was possible to reveal it and correct it.
This happened when Aaron connected with Moses, and in their work together, they reached a state during which the Upper Light descended on them clothed in the characteristic of bestowal. In this way, by approaching each other, they acquired the characteristic of bestowal.
From KabTV’s “Secrets of the Eternal Book” 1/15/13