In this week's parsha we learn about the diagnosis and treatment of "tzoraas" (a leprous disease, which one would suffer because of some moral failing) by a kohen. The kohen might observe a whitish sore on the person's skin, and, if he diagnosed it as "tzoraas", he would declare the person "tamei" [inadequately translated as "unclean" or "impure"]. In general, the whiter the sore, and the larger the area it covered, the more "tamei" the person would be; but -- and here is a remarkable thing -- once the sore covered the whole body, the person became "tahor" ["clean", "pure"] again! (Lev. 13:13)
How can we explain this? The Gemara (Sanhedrin 97.) quotes R' Yitzchak as saying that the Messiah will not come until all the governments of the world will have become heretical. His pupil Rabba says: Where did he learn this from? From the above verse. (meaning: everything will be bad before good can come.)
Well, that was not much of an explanation of our original puzzle! If anything, it made it more puzzling.
I cannot claim to give a complete explanation, since the laws of purity and impurity are difficult to understand, but perhaps we can give some clue to the situation.
There is a story in the Gemara (Avoda Zara 17.) about a certain Eliezer ben Durdaya, who visited every house of sin that he could. One day he heard of a prostitute who lived overseas, and was very expensive. He collected the money, and sailed "across seven seas" to visit her. While they were together, she suddenly started to berate him about his lifestyle, saying "Eliezer ben Durdaya, there is no hope of forgiveness for you!" (Many questions arise here: What moved her to admonish him thus? How could she know that there was no hope of forgiveness for him? And who was she to talk? But let us leave these questions aside for now.)
Eliezer, hearing this from her, fled to the countryside. He said to the mountains and valleys: "Pray for mercy for me!" But they responded: "We cannot, we are busy praying for mercy for ourselves." He made the same request of the sun and moon, and the stars, but they gave the same answer. Finally he exclaimed: "I see that my salvation depends on no one but me!" He lowered his head between his knees screamed out with cries of anguish and died. At that moment, a heavenly voice said: "Rabbi Eliezer ben Durdaya, there is a place for you in the world to come."
What can we make of this story? The best way to approach G-d is through years of hard work, improving oneself. But in some cases, teshuva (penitence) can come quickly (although never easily). Eliezer ben Durdaya only rose to teshuva after he had fallen as low as he could. We must be careful here -- this does not mean that someone can deliberately sin, with the idea of doing teshuva afterwards! (The Rambam speaks explicitly against this.)
If Eliezer ben Durdaya had deliberately sinned with such an idea in mind, his teshuva would never have been accepted. But sometimes it can happen that someone who is steeped in sin becomes so disgusted with himself that he reacts against his behavior, and finds the energy to lift himself up to a more virtuous life. The very lowliness of his situation serves somehow as the inspiration to drastically better himself.
In Koheles (7;20) it says: "There is no tzaddik who has only done good and never sinned." The Gra comments: Why does it include the phrase "has done only good"? Why not just say: "There is no tzaddik who has never sinned?" The reason, says the Gra, is that it means that every tzaddik has done at least some good as a result of some sin.
This, I suggest, is the explanation for the puzzle we started with. The spread of the leprous sore reflects the spread of sin in the soul of the sufferer. When it reaches a certain point, with the sore covering the whole body, the soul reacts to its sinful state, rises to teshuva, and the person is pure again. The Torah tells us that a tzaddik must fall seven times, and then he may rise (Proverbs 24:16). Sometimes it is possible that the path upwards entails some falling. The fall is one step closer in the direction upward.