Hashem wanted Moshe to instill Aharon with the feeling that he was being appointed to this prestigious position because of his elevated status. If Moshe would have commanded Aharon to fulfill his Priestly obligation without persuading him to take the position, the honor and prestige of the position would have been adversely affected. The message Moshe conveyed would have been that the position was purely ministerial in nature, not possessing its own innate sense of importance. An honor can only be conferred upon a person with his acquiescence. Forcing him to accept it diminishes the importance of the person and consequently the prestige of the position.

1.8:2

Question of the Week:

The Talmud refers to a regular Kohein vis-à-vis the Kohein Gadol as a Kohein “hedyot”. The term hedyot has a disparaging connotation. Why would Chazal use that particular appellation to describe the Kohein?