Moses told Aaron, "Come close to the altar." (9:7) Rashi states: Aaron was reserved and afraid to come close. Moses said to him, "Why are you reserved? For this you were chosen."
The Baal Shem Tov explains Rashi's comments in the following manner: You were chosen for this - because of your reserve and modesty, and your doubts about being worthy to carry out the Divine service. These are the qualities that demonstrate your being fit for the job. (L'Chayim)
Reprinted from this week’s email of R’ Yedidye Hirtenfeld’s whY I Matter parsha sheet for the Young Israel of Midwood in Brooklyn.