All of Leviticus is primarily addressed to the priesthood, but Leviticus 21 is about qualifications of the High Priest, not regular priests or the lay Israelites. There are things that other Israelites can do, within limits that are totally forbidden to the High Priest. His family, descendants of Aharon (Aaron) is held to a higher standard than other families. This chapter also shows us how holy — set apart — our High Priest, Yeshua, was to be.