Charles Ellicott Commentary Leviticus 9:1

"And it came to pass on the eighth day, that Moses called Aaron and his sons, and the elders of Israel;" — Leviticus 9:1 (ASV)

And it came to pass on the eighth day. —That is, the day following the seven days of consecration. According to ancient tradition this was the first of the month Nisan, or March.

Moses called Aaron and his sons, and the elders. —That is, the same elders, the representatives of the people, who were called to attest the imposing ceremony of consecration , are now also summoned to witness how the newly-installed priests entered upon the active duties of their ministrations. Like newly-born children who remain seven days in a state of uncleanness and enter into the covenant privileges of the congregation on the eighth day , so the newly-created priests after a purging of seven days commenced their sacred duties and partook of their privileges on this symbolical day.