If a person will on the skin of his flesh... an affliction of tzoraas, he shall be brought to Aharon the Kohen, or to one of his sons the kohanim. (13:2)
Why is the treatment of tzoraas, a matter that is ostensibly medical in nature, entrusted to the kohanim?
The straightforward answer, says Meshech Chochmah, is that since the condition of tzoraas and the recovery therefrom involves bringing the person from a state of tumah to taharah (purity and impurity), it lies in the domain of the Kohen. Indeed, the Gemara associates tzoraas in this regard with the procedure of parah adumah (red heifer), which is also entrusted to the Kohen, even though it is technically not a korban, nor are its procedures done in the Beis Hamikdash. Nevertheless, since the parah adumah is instrumental in allowing a person to go from a state of tumah to taharah, it is performed by the Kohen. The same is true for tzoraas.
On a deeper level, the Meshech Chochmah explains that although tzoraas befalls a person on account of his wrongdoings, it is nonetheless also a contagious disease. Thus, we find that the sages of the Talmud would take care to avoid enclaves where people with tzoraas were situated.
Indeed, on a basic level, this is what is behind the Torah’s instruction that the metzora announce that he is tamei as he is leaving the city, in order to warn people to keep their distance so that they not catch his tzoraas.
In light of this, we will appreciate that whoever treats the metzora is effectively exposing himself to danger of contracting tzoraas, and will thus be in need of special protection to avoid this occurring. It is for this reason the Torah places the metzora’s treatment in the domain of the kohanim, for, having been separated from the rest of the people to enter Hashem’s domain, they are subject to a higher level of Divine supervision, and will thus be vouchsafed from harm in their interaction with the metzora.
