Leviticus 9:7

Go and offer — Moses had hitherto sacrificed, but now he resigns his work to Aaron, and actually gives him that commission which from God he had received for him. For thyself and for the people — The order is very observable, first for thyself, otherwise thou art unfit to do it for the people. Hereby God would teach us, both the deficiency of this priesthood, and how important it is that God's ministers should be in the favour of God themselves, that their ministrations may be acceptable to God, and profitable to the people.