Razor used by Leviyim, Nezirim and Lepers

Question

וְכֹֽה־תַעֲשֶׂ֤ה לָהֶם֙ לְטַֽהֲרָ֔ם הַזֵּ֥ה עֲלֵיהֶ֖ם מֵ֣י חַטָּ֑את וְהֶעֱבִ֤ירוּ תַ֙עַר֙ עַל־כָּל־בְּשָׂרָ֔ם וְכִבְּס֥וּ בִגְדֵיהֶ֖ם וְהִטֶּהָֽרוּ׃ This is what you shall do to them, to purify them; sprinkle them with the sin-offering waters, and cause a razor to pass over (shave) their entire bodies, and they shall wash their garments and purify themselves

Masechta Nazir 40a

תנן התם שלשה מגלחין ותגלחתן מצוה נזיר ומצורע ולוים וכולן שגילחו שלא בתער או ששיירו שתי שערות לא עשו ולא כלום § We learned in a mishna there (Nega’im 14:4): Three types of people must shave their hair, and their shaving is a mitzva: A nazirite; and a leper, as it is stated: “And he who is to be cleansed shall wash his clothes, and shave off all his hair” (Leviticus 14:8–9). And the third category is Levites, when they were first sanctified for their service, as it is stated: “And this you shall do to them to cleanse them: Sprinkle the water of purification upon them, and let them cause a razor to pass over all their flesh” (Numbers 8:7). And with regard to all of them, if they shaved with an implement other than a razor, or if they left two hairs uncut, they have done nothing, i.e., they have not fulfilled their obligation.

It appears that Leviyim Nezarim and Lepers can use a razor but why can’t anyone other than these three use a razor?

Answer 1

The gemara you reported in Nazir 40a taught that Leviim, Nazir and Metsora have a mitsva to shave with a blade(1). This is a Mitsvat asse, the Mitsvat asse pushes out the mitsvat lo taasse, the prohibition of shaving beard with a blade for metsora and leviim who need to shave the beard and of shaving temporal scalp for the nazir who shave the scalp only.

So, without a special mitva from Torah to shave with a blade, nobody, no leviim, no Metsora not at the time of shaving, no nazir not at the time of shaving can make what the mitsvat tiglachat orders.

(1): For Leviim במדבר ח,ז

וְכֹֽה־תַעֲשֶׂ֤ה לָהֶם֙ לְטַֽהֲרָ֔ם הַזֵּ֥ה עֲלֵיהֶ֖ם מֵ֣י חַטָּ֑את וְהֶעֱבִ֤ירוּ תַ֙עַר֙ עַל־כׇּל־בְּשָׂרָ֔ם וְכִבְּס֥וּ בִגְדֵיהֶ֖ם וְהִטֶּהָֽרוּ׃‏

For Nazir (see Nazir 39b), במדבר ו, ה

כׇּל־יְמֵי֙ נֶ֣דֶר נִזְר֔וֹ תַּ֖עַר לֹא־יַעֲבֹ֣ר עַל־רֹאשׁ֑וֹ עַד־מְלֹ֨את הַיָּמִ֜ם אֲשֶׁר־יַזִּ֤יר לַיהֹוָה֙ קָדֹ֣שׁ יִהְיֶ֔ה גַּדֵּ֥ל פֶּ֖רַע שְׂעַ֥ר רֹאשֽׁוֹ׃ ‏

This teaching is needs Gemara to be understand, below an extract of Gemara and Rivan's comment

לפי שלא למדנו לתגלחת האחרונה [שיהיה בתער] - של טהרה לאחר תשלום ימי נזירות שיהא בתער לפי שלא כתב אלא וגילח את שער ראש נזרו לכך כתב לך תער כאן שאינו צריך ללמדך שאותה תגלחת לא תהא אלא בתער:‏

To teach that the prohibition of cutting hair for nazir with blade only is not right (se Gemara), so why the verse writes "blade", it is unnecessary? To teach that the finally cutting hair of the Nazir needs to be with a blade.

Metsora is deducted from Nazir and Leviim.