Excerpt from Degel Machaneh Ephraim, Parshas Shemini (via BaalShemTov.com) :
And Moshe said to Aharon: Draw near to the altar. (Shemini 9:7)
Rashi comments that Aharon was ashamed and afraid to draw near to the altar. Moshe therefore said to him, Why are you ashamed? You were chosen for this.
This is a surprising explanation. Just because he was chosen doesn't mean that he should not be ashamed.
Rather, I heard from my grandfather [the Baal Shem Tov] this explanation: Moshe said you were chosen precisely because you feel fear and shame before G-d, for the sacrifices of G-d are a broken spirit. (Tehillim 51:19)