Why a person was punished with a tzara’at (leprosy style) affliction is the subject of much discussion amongst the Sages of the Talmud (see Arachin 16a) and within Midrashic literature (Midrash is the earliest form of Rabbinic commentary on the Bible).
The Kli Yakar (Rabbi Shlomo Ephraim Lunshitz d. 1619) focuses on three main reasons, which are the most strongly hinted to in the verses.
Our starting point is that the word metzora, used to describe someone afflicted with tzara’at, is made up of two words – motzi and ra, meaning ‘bringing out bad’, implying that this affliction brought out into the open negativity that was within a person. People would now know to avoid him. This also acted as a drastic call for the metzora himself to change his ways.
What are the three areas of wrongdoing that this malady brought to the fore? The most well known is lashon ha’ra – speaking negatively about others. Consequently, as part of his purification process, the metzora had to sacrifice two birds. The chirp and chatter of these animals reminded him of how he misused his power of speech.
The second reason cited by the Kli Yakar is tzara’at ayin – stinginess, either an unhealthy desire for money or an unwillingness to share with others. Therefore, the Cohen would come to the metzora’s house and take out his possessions for the public to see.
The third cause is arrogance. To address this problem, cedar wood and hyssop were tied around the metzora’s bird offering; having been as haughty as a high tree, he now had to humble himself to be like a lowly herb.
These three negative traits are hinted to in the three words the verse uses to describe tzara’at: “If a man will have on his flesh a s’eit, or sapachat or baheret…” (Vayikra 13:2)
S’eit can mean ‘raised’, hinting to the afflicted individual that he may have displayed haughtiness. Sapachat means ‘secondary’, a hint to money; whilst actions and character development will accompany a person into the world to come, his possessions will not – they are in essence ‘secondary’. Finally, baheret can mean ‘whiteness’; one who speaks badly about others shames them, causing the blood to drain from their face.
The metzora would have to go to a Cohen to oversee his purification. Every Cohen is a descendant of Aharon, whose characteristics were the exact opposite of these three traits. He was the epitome of humility, happily accepting that his younger brother Moshe (Moses) should lead the Jewish people (see Shemot 4:14). Whilst speaking badly leads to quarrelling, Aharon, in contrast, loved and pursued peace, attempting to rectify disputes (see Pirkei Avot 1:12). Moreover, a Cohen had no land of his own, having to make do with whatever he was given, leaving little temptation to guard possessions.
The Kli Yakar concludes this idea beautifully in a later comment (14:9) when discussing the metzora’s obligation to shave off the hair of his head, beard and eyebrows. The head is the place of arrogance. The hair on his beard, which surrounds his mouth, was shaved to atone for its misuse and the eyebrows to compensate for having had a stingy attitude.