The last thing that Moses must do before opening the Tabernacle for its first day of business is to appoint the priests. It is interesting to note that Aaron wasn’t biting at the bit to begin his work as the High Priest.  

God tells Moses to “take him” and Rashi comments that this means he had to convince Aaron of the new duties he and his children had to perform.

It is exceedingly strange that Aaron, a very holy man himself, should not have wanted to take on the honour of being the High Priest. Of all the High Priests recorded in the Bible, Aaron is certainly the paragon.

The purpose of the High Priest was to unify the people and no one unified others like Aaron. If this is the case, why does Aaron want to shirk his duties?  This was the position he was created for.

The Vilna Gaon writes that Aaron felt guilty because of his involvement in creating the Golden Calf, which the Jews served a few Torah portions ago. This service had terrible implications for the Jewish people and Aaron felt guilty for his part in it. Moses therefore must convince Aaron that this one action does not invalidate him from the job he was born to perform.
 
Guilt is a very powerful psychological force in that it has the potential to create two different outcomes. It can paralyse and continue the status quo, or it can motivate away from past behaviour to future improvement. Aaron is told to become involved in his new work, not to let his past demoralise him, but to allow it to motivate him to be a better High Priest.
 
The power of guilt lies in the potential for growth and change. The moment it immobilises us is the moment that guilt becomes toxic. Our task is to motivate our guilt — let it work for us, rather than let it control our life.