What will be the Din if two green or red hairs grow in the Nesek?
Why does the Torah write "Vese'or Shachor Tzamach bo", seeing as it is La?av Davka black hairs (see Torah Temimah, note 153)?
Sifra: To include two black hairs that grew later at the beginning and two black hairs that were there at the end. 1
See Torah Temimah, note 153.
What is the word "Tzamach Bo" coming to preclude?
Sifra: It precludes the necessity for the hairs to be surrounded by the Nega. 1
See Torah Temimah, note 154.
Why does the Torah insert the (otherwise superfluous) phrase "Nirpa ha'Nesek"?
Sifra: To preclude where a second Nesek appeared around the black hairs, in which case the black hairs are not a Si'man Taharah.
Oznayim la'Torah (citing the Rambam): To teach us that, even if, after the black hairs disappear, the yellow hairs or the Pisyon remain, he is Tahor - unless new Simanim appear on the skin.
Why does the Torah add the (otherwise superfluous) words "Tahor Hu"?
Rashi: To teach us that if the Kohen declares Tahor a person who is Tamei, he is not Tahor 1 (and that the Metzora is only Tahor after the Kohen declares him Tahor - Sifra).
Sifra: To teach us that he is Tahor even if the black hairs fall out. 2
What will be the Din if only one of the conditions is fulfilled (the Nesek did not grow, and black hair did not grow in it, or it grew, and black hair grew in it)?
Having already taught us that if it did not spread he is Tahor, why does the Torah need to say "ve'Im be'Einav Amad"?
Da'as Zekenim: Perhaps it is to teach us that black hairs in the middle are Metaher.
QUESTIONS ON RASHI
Rashi writes that "ve'Se'ar" teaches us that also two yellow or red hairs in the Nesek are a Siman Taharah. How does he learn it from there?
Perhaps Rashi explains like R. Yonason (refer to 13:37:151:1) that we explain the prefix 'Vav', since the Torah could have written 'O Se'ar' (PF).
Rashi writes that if the Kohen declares Tahor a person who is Tamei, he is not Tahor. But neither is one Tamei until the Kohen declares him Tamei?
Divrei David: Indeed, Rashi means that once the Kohen realizes his mistake, he is obligated to declare him Tamei, but until he does, he is Tahor. Conversely, if he was Metamei a Tahor and realized his mistake, it is as if he did not say anything, so he is Tahor.
Toras Moshe: If the Kohen erred in Shikul ha'Da'as (he ruled unlike the primary opinion) and was Metaher, and later retracted or a bigger Chacham persuaded him to retract, the Nega is Tamei retroactively. 1 Automatically, if he erred in Shikul ha'Da'as and was Metamei, he is Tamei retroactively.
This Drashah is limited to the case of our Pasuk - one who was Tamei, and the Kohen mistakenly declared him Tahor. His words have no effect, and he is still Tamei. 2
