The skin diseases falling under the category or tzarras (often translated as “leprosy”) needed to be determined by a kohein (Leviticus 13:1-2). Yet, the so-called “plague of leprosy,” as mentioned in the Tanach, is not exactly the leprosy of more modern times. Rather, it is a category of various skin diseases that need to be determined by the Kohein: for only the Kohein has the authority to make the pronouncement. “And the [kohein] priest shall look on him and pronounce him unclean” (Leviticus 13:3, JPS).
The leprosy of biblical times was the result of spiritual malaise, commonly, the result of lashon harah (literally, evil tongue – a type of gossip). “The word, metzorah (someone, who has tzaaras – leprosy) is a contraction of motzi ra, meaning, “one who spreads slander” (Arachin 15b). The very visible chastisement is meant to show that the metzorah must mend his ways. In other words, the outward sign is meant to compel him to do teshuvah (repentance).
Sin may be manifest in our lives, living below the surface of our awareness. For this reason, one must make an attempt to examine one’s life. There are visible signs, at times, that we need to understand as wake-up calls. Also, when the children of Israel entered the land, sometimes they found mold in the walls; so, they would have to dig out the mold. On the one hand, the nega (plague) in the form of mold should serve for them to search their conscience, on the other hand, they often found hidden treasures in the walls, hidden by the previous occupants, the Canaanites, who hoped to return. By way of an analogy, there is always a reward for rectifying our faults.