Tazri'a discusses a now-extinct disease known as tzara'at, which appeared on a Jewish man or woman's skin, garment, or home as a reflection of some subtle spiritual imperfection in the person.
In the case of a dermal lesion, the person was brought to a kohen (priest) for an examination. If the priest declared that the person was indeed suffering from tzara'at, the sufferer needed to go through a period of separation from the community followed by a process of ritual purification.
Leviticus 13:6
It would seem more logical that someone with a lesion be brought to an expert in Jewish law to determine if he is indeed afflicted with tzara’at, why a priest?
The reason why the Torah specifies that a priest make this determination is because the priests are devoted totally to the service of G-d. Their holiness-centered lifestyle keeps them immune from the worldly perspective that sees every effect as the deserved result of some cause. Thus, they are uniquely positioned to see the good in others and enable them to see the good in themselves. This is what eventually heals the person from tzara’at.
Similarly, whenever we confront a potential spiritual defect in ourselves, we must access our inner “priest,” our pristine connection to G-d, in order to view that defect in a way that will lead to its healing. If we find it difficult to summon our own inner priest, we should seek out someone who can substitute for it, in order to cure ourselves in a wholesome and positive manner.
—from Daily Wisdom 3