Exodus 29:35

And thus shall thou do unto Aaron, and to his sons,.... For their consecration, washing, clothing, anointing them, sprinkling blood upon them and their garments, and offering sacrifice for them:

according to all things which I have commanded thee; no one thing was to be omitted, and we find they were carefully and punctually observed, Leviticus 8:1

seven days shalt thou consecrate them: so long the rites and ceremonies of the consecration were to be performing, that they might be thoroughly used to the putting on of their garments, and the offering of sacrifices as they saw performed by Moses; and in all respects be fitted for the discharge of their office: the Jewish writers generally say that seven days were appointed, that a sabbath might pass over them.