John Wesley on Leviticus 9:1

On the eighth day - Namely, from the day of his consecration, or when the seven days of his consecration were ended. The eighth day is famous in scripture for the perfecting and purifying both of men and beasts. See Lev 12:2,3 14:8,9,10 15:13,14 22:27. And the elders of Israel - All the congregation were called to be witnesses of Aaron's installment into his office, to prevent their murmurings and contempt; which being done, the elders were now sufficient to be witnesses of his first execution of his office.