Commento su Levitico 13:11

צרעת נשנת הוא IT IS AN OLD LEPROSY — i. e. it is an old leprous malady beneath the sound flesh, and this wound appears healthy above, but underneath it is full of moisture (pus), therefore the priest shall pronounce it unclean. Scripture states this in order that you should not say: since healthy flesh has come over it I shall pronounce it clean.

It has produced healthy [flesh], I will declare it clean. Re’m writes: This raises a strong difficulty: From here it implies that healthy flesh is a sign of purity, and therefore one [might] say: “Since it has produced healthy [flesh], I will declare it clean.” Above, however, Rashi says: “Or there is healthy flesh” — “This too is a sign of uncleanness...”! It appears to me that Rashi is coming to answer why does Scripture need to write: “It is an old tzora’as...” It should have written only, “or there is healthy flesh in the spot of intense whiteness, and the kohein shall declare him unclean.” Rashi answers that Scripture itself comes to give the reason why we declare him impure when he has healthy flesh, [since,] on the contrary, he should be declared pure because the skin-eruption has begun to heal since it has healthy flesh. For this reason Scripture explained: “It is an old tzora’as.”

צרעת נושנת, “an old tzoraat;” Rashi here is not precise enough in his commentary. In Torat Kohanim a white hair is considered as proof of ritual contamination of the skin from which it grows. Similarly what is described by the Torah as michyeh, i.e. מכות מחיה, in verse 24, is a sure sign of ritual impurity, regardless of any changes from one week to another. The fact that it too is treated by the Torah as feminine, is clear proof of this.

צרעת נושנת היא, “it is an old plague,” it had only appeared to have healed by new skin covering it. Beneath that new skin the flesh had remained raw and moist. The Torah had to inform us of this so that we would not think that the surface of the skin is the only determining factor. That is not enough for the priest to declare the afflicted person as ritually pure. (Compare Rashi)