‘And he said to Aaron, “Take a calf of the herd for a purification for sin offering, and a ram for a whole burnt offering, without blemish, and offer them before Yahweh.” '
It is noteworthy that instead of the mature bull ox (Leviticus 4:3) Aaron is to offer a bull calf for his own purification for sin offering. This is the only time when a calf is offered. Some see it as having in mind his failure with respect to the golden calf (Exodus 32:4) which is now especially atoned for. But the significance may rather lie in the fact that this is not for a particular sin, nor is it to cleanse the Holy Place. His priesthood is yet in its infancy. He has not yet failed as a priest, and he has not yet entered the Holy Place, and a bull ox has already been offered for him in 8:14. Thus the bull ox here is younger, and in its infancy. (It may also have had the practical purpose that it would take less time for the flames to consume it, with so much to follow).
With it he will offer a ram for a whole burnt offering as in his consecration. Both are to be without blemish. They are to be offered to Yahweh.
When we consider the process of consecration that he and the priests have already gone through it makes us recognise that none of these sacrifices could really deal with the problem of sin. Continually therefore the fact of his sinfulness has to be brought before God, and the means provided by which he can find ceremonial purification and atonement. Really, like all who were accepted in Old Testament days, they were accepted by the unmerited love and compassion of God, with in mind the Great Sacrifice yet to come.
And as Aaron and his sons had to offer purification for sin and whole burnt offerings for themselves constantly before Yahweh, so are we to come continually into His light and seek for the blood of Jesus Christ, God's Son, to cleanse us from all sin (1 John 1:7), and to continually rededicate ourselves to His service. It is a reminder that while on earth none of us are wholly free from the tyranny of sin. The one who thinks that he stands, should ever take heed lest he fall.