It is necessary to form a rationale for the Torah‘s demand that the Kohain personally supervise all of the ritual concerning the leper. Why does the Torah emphasize this at each step of the purification process? The Talmud (Erchin 16a) lists the various reasons for the affliction of leporsy, such as haughtiness, slander, stinginess, etc… These are sins which by their very nature indicate one’s pride in himself. Such an individual sins because he thinks that he controls his own destiny. He looks down on others who may have certain faults, because he does not have the sensitivity to help another fellow human being. Hashem will therefore inflict this individual with leprosy, causing him to live in seclusion. He will then have to perform certain deeds for his purification process in order to remind him and make him acknowledge his sins. This will ultimately cause him to reflect upon his life, and guide him in its proper course, so that he will be cognizant of Hashem’s presence in every area of his life. Only a Kohain can demonstrate this lesson, for the Kohain, does not have any possession of his own in Eretz Yisroel. He is at the mercy of others, because of his being dependent upon their goodwill for his sustenance. The Kohain is one who realizes that his sustenance comes directly from Hashem, and it is through his example that the leper can be brought to repent and correct his misguided and foolish ways.
