Leviticus 9:1,2

And it came to pass on the eighth day, that Moses called Aaron and his sons, and the elders of Israel;

Moses called ... Take thee a young calf. The animals used in sacrifice were not only to be without blemish, but, excepting doves, not under eight days, nor over three years old. The directions in these sacred things were still given by Moses, the circumstances being extraordinary. But he was only the medium of communicating the divine will to the newly-made priests.

The first of their official acts was the sacrifice of another sin offering, to atone for the defects of the inauguration services; and yet that sacrifice did not consist of a bullock-the sacrifice appointed for some particular transgression; but of a calf, perhaps not without a significant reference to Aaron's sin in the golden calf.

Then followed a burnt offering, expressive of their voluntary and entire self-devotement to the divine service. The newly-consecrated priests, having done this on their own account, were called to offer a sin offering and burnt offering for the people, ending the ceremonial by a peace offering, which was a sacred feast. This injunction 'to make an atonement for himself and for the people' (Septuagint, 'for thy family') at the commencement of his sacred functions furnishes a striking evidence of the divine origin of the Jewish system of worship.

In all false or corrupt forms of religion the studied policy has been to inspire the people with an idea of the sanctity of the priesthood, as, in point of purity and favour with the Divinity, far above the level of other men. But among the Hebrews the priests were required to offer for the expiation of their sins, as well as the humblest of the people. This imperfection of Aaron's priesthood, however, does not extend to the Gospel dispensation; because our Great High Priest, who has entered for us into 'the true tabernacle,' 'knew no sin' (Hebrews 10:10).