On the eighth day Moses summoned Aaron and his sons and the elders of Israel.
1. And it came to pass on the eighth day We have here related how Aaron and his sons, after the time of their consecration was fulfilled, began to execute their office. It was necessary that He should be his brother’s disciple, in order to follow the pattern laid down by God.
Orders are here given for another solemnity upon the eighth day; for the newly-ordained priests were set to work immediately after the days of their consecration were finished, to let them know that they were not ordained to be idle: He that desires the office of a bishop desires a good work, which must be looked at with desire, more than the honour and benefit.
Commenting on Leviticus 9:1-7
And it came to pass on the eighth day,.... When the seven days of consecration were ended, as Ben Gersom, the day following them, so soon was Aaron called to the execution of his office; and so both the Targum of Jonathan and Jarchi make it to be the eighth day of the consecration, or the day after the anointing of Aaron and his sons...