John Calvin 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. Here it is related how Aaron and his sons, after the time of their consecration was completed, began to carry out their duties.

It was necessary that he should be his brother’s disciple, to follow the pattern established by God. We must also bear in mind that Moses, who was not appointed priest by a solemn rite, consecrated the others, so that the authority and effectiveness of the outward sign would rest in God alone.

Therefore, the earlier part of the chapter details how, after Aaron had been initiated into the priest’s office for seven days, he began the work entrusted to him by God’s command. The second part shows how the sacrifices were approved by a divine miracle, ratifying the priesthood that God had instituted.

But first of all, He enumerates the ordinary kinds of sacrifice: namely, for sin; the burnt offering; and for thanksgiving, the sacrifice with the meat offering (minha) and the sprinkling, so that in every respect Aaron might be recognized as the lawful priest of God.