He was a truly pious person who loved God and yearned to serve Him. He saw so much activity going on around him in preparation for the dedication of the sanctuary in the wilderness, and he felt slighted and left out because he had not been asked to bring a gift or donation.
His depressed state of mind is described by Rashi, who links it with the opening verses of the sidra, in which God tells Moses to pass on to Aaron the news that it would be he who had the culminating honour, to kindle the lamps of the menorah (Num. 8:1-3).
Not only would Aaron light the menorah, but it would be his descendants’ task throughout history (Ex. 27:21)