And furthermore, if it should enter your mind that when he performs his shaving with tweezers or a plane he performs a mitzva, from the fact that the word razor is not written he should not be allowed to use a razor at all, in accordance with the opinion of Reish Lakish, who says a principle in this regard.

The Gemara cites the relevant principle: Any place where you find a positive mitzva and a prohibition that clash with one another, if you can find some way to fulfill both, that is preferable; and if that is not possible, the positive mitzva will come and override the prohibition. In this case the leper can fulfill his duty with tweezers or a plane, and therefore it should be prohibited for him to shave with a razor. Since it was necessary for the verse to say that the positive mitzva for a leper to shave overrides the prohibition against destroying one’s beard, this proves that the mitzva can be performed only with a razor.

The Gemara asks: And Rabbi Eliezer, what is his reason? From where does he derive the halakha that a leper must use a razor? He derives it from the fact that the verse states with regard to a leper: “He shall shave all his hair off his head and his beard” (Leviticus 14:9). As it is taught in a baraita: Why does the verse state: “His head,” if it already stated: “All his hair”? It is because it is stated with regard to a nazirite: “No razor shall come upon his head” (Numbers 6:5), and therefore one might have thought that the same should also apply to a nazirite who is a leper, i.e., it should be prohibited for him to shave his head even for the purification ritual for his leprosy. Therefore, the verse states: “His head,” to teach that a nazirite who is a leper must shave his head with a razor. Being that a nazirite is prohibited only to use a razor, if a leper could fulfill his obligation to remove his hair using other implements, a nazirite who is a leper would not be permitted to use a razor. Therefore, it can be inferred from the halakha of a nazirite who is a leper that the only way for a leper to remove his hair is with a razor.

The Gemara rejects this suggestion: And from where do you know that a leper must shave his head with a razor? Perhaps even if he actually removed it with tweezers or a plane he performs a mitzva. And if you would say: If so, why do I need the verse to teach me that he uses a razor, through the derivation of the superfluous term “his hair,” as above, one can answer: That is to say that he is permitted to shave even with a razor. As, it might enter your mind to say that since with regard to a nazirite, when he performs the act of shaving with a razor he is liable for transgressing the prohibition, with regard to a nazirite who is a leper as well, he should also be liable even if he shaved for his leprosy. The verse therefore teaches us that this is not the case, but it does not teach that a leper must use a razor.

The Gemara rejects this suggestion: If it should enter your mind that when a leper performs his hair removal with tweezers or a plane he performs a mitzva, then from the fact that the verse did not explicitly write: Razor, it can be inferred that he is not allowed to use one, in accordance with the aforementioned principle of Reish Lakish that one may not violate a prohibition, even for the sake of a mitzva, if it is possible to perform the mitzva in a different manner. Rather, the verse must be coming to teach that the mitzva of the shaving of a leper can be fulfilled only with a razor.

The Gemara asks: And the Rabbis, with regard to this term: “His head,” which is referring to a leper, what do they learn from it? The Gemara answers: They require this term to override the prohibition of rounding the corners of the head. As it is taught in a baraita with regard to the verse “You shall not round the corners of your heads” (Leviticus 19:27): One might have thought that the same should also apply to a leper, that it should also be prohibited for him to round the corners of his head when he shaves. Therefore, the verse states: “His head,” with regard to a leper.

The Gemara asks: Why do I need the Torah to write: “His head”? And let one derive this halakha that the mitzva of shaving overrides that prohibition from the term “his beard” (Leviticus 14:9). As it is taught in a baraita: Why does the verse state: “His beard”? It is because the verse states with regard to priests: “Neither shall they shave off the corners of their beards” (Leviticus 21:5), and therefore one might have thought that the same prohibition against shaving one’s beard should also apply to a leper. Therefore, the verse states: “His beard.”

The Gemara asks: If so, why do I need the Torah to write: “His head,” and why do I need it to write: “His beard”? One source should suffice to teach that the shaving of a leper overrides any prohibitions that would be violated by that act. The Gemara answers: Both verses are necessary. As, had the Merciful One written only: “His beard,” and not written: “His head,” I would say that the rounding of the entire head, i.e., shaving all the hair off one’s head and not merely the sides, is not called a prohibited rounding. If that were so, the shaving of a leper’s head would not be prohibited by Torah law. For this reason the Merciful One writes: “His head,” to teach that the shaving that the leper performs would be considered a prohibited rounding of the head had the Torah not commanded him to shave.