Adam Clarke on Leviticus 22:2

Speak unto Aaron and to his sons, that they separate themselves - The same subject is continued in this chapter as in the preceding, with this addition, that besides the perfection of the priests, it was indispensably necessary that the sacrifices also should be perfect. In the service of God, according to the law, neither an imperfect offering nor an imperfect offerer could be admitted. What need then of a mediator between a holy God and sinful men! And can we expect that any of our services, however sincere and well-intentioned, can be accepted, unless offered on that living Altar that sanctifies the gift?