IS SHAVING A MITZVAH?
(R. Chiya): Tiglachas Metzora cannot count for Tiglachas Nazir Tamei, for a Metzora shaves before immersing, and a Nazir Tamei shaves after immersing;
Tiglachas Metzora cannot count for the shaving of a Tahor Nazir, for a Metzora shaves before offering Korbanos. A Tamei Nazir shaves after Korbanos.
(Mishnah): Tiglachas Metzora...
Question (Rami bar Chama): Are (all) four shavings Mitzvos, or (is the third) merely to remove hair (some of which grew while) Tamei?
If it is only to remove Tamei hair, a Ta'ar is not needed. A cream may be used to remove the hair.
Answer (Rava - Beraisa): He shaves four times.
If (the third) shaving is only to remove Tamei hair, it would suffice to shave three times!
Conclusion: Even the third shaving is a Mitzvah.
WHO MAY BECOME A NAZIR?
(Mishnah): Nezirus does not apply to Kusim. It does apply to women and slaves. (Note: 'Kusim' were Nochrim who converted because they were being eaten by lions, but they observed only some Mitzvos and continued to serve idolatry. Here, Kusim refers to Nochrim. (The Rosh's text said explicitly says so.))
There is a stringency of women over slaves. One can force his slave to transgress Nezirus, but he cannot force his wife.
(Gemara) Question: What is the source that Kusim cannot be Nezirim?
Answer (Beraisa #1): "Speak to Bnei Yisrael", not to Kusim. "And say to them" includes slaves.
Question: Why must a verse include slaves?
Every Mitzvah that applies to women applies to slaves!
Answer (Rava): It says regarding vows "to forbid on one's soul." This refers to one who owns his own soul. This excludes slaves;
If not for a verse to include them, we would say that they also cannot accept Nezirus.
(Beraisa #1): "Bnei Yisrael" - and not Kusim...
Question: Sometimes the Torah says Bnei Yisrael, and we do not exclude Kusim!
Regarding Erchin (vowing to give money to Hekdesh, based on a person's age and gender) it says Bnei Yisrael;
(Beraisa): Bnei Yisrael can vow to give a person's Erech, but Kusim cannot.
Suggestion: Perhaps one cannot vow to give the Erech of a Kusi!
Rejection: "A man" (includes Kusim).
Answer #1: Another verse excludes Kusim from Nezirus - "for his mother and father he will not be Metamei."
This shows that Nezirus applies only to one who has a (Halachic) father; this excludes Kusim.
Question: It what sense does a Kusi not have a father?
Answer #1: He does not inherit his father.
Objection: R. Chiya bar Avin taught that "I gave Mount Se'ir to Esav for an inheritance" teaches that a Kusi inherits his father mid'Oraisa!
Answer #2: He has no Mitzvah to honor his father.
Objection: Parshas Nazir does not discuss honoring a father!
Answer #3: "For his mother and father he will not be Metamei" - Nezirus applies only to one who can become Tamei. This excludes Kusim.
Question: What is the source that Kusim cannot become Tamei?
Answer #1: "A man who will be Tamei and will not Metaher himself will be cut off from the congregation" - Tum'ah applies only to members of the congregation. This excludes Kusim.
Rejection: Perhaps Kares applies only to members of the congregation, but even others can become Tamei!
Answer #2: "The Tahor will sprinkle on the Tamei" - only one who can become Tahor can be Tamei! (Taharah through the red heifer is for "Bnei Yisrael.")
Rejection: Perhaps he can become Tamei, but he cannot become Tahor afterwards! (This verse is not extra. The coming verse is extra.)
Answer #3: "A man who will be Tamei and will not Metaher himself" (only one who can become Tahor can become Tamei).
Defense (of Answer #1 - Rav Acha bar Yakov): (Regarding Tum'as Nazir, the Torah discusses a father who bequeaths everything, even slaves - ) "You will bequeath (your slaves) to your children after you";
Since a Kusi cannot inherit slaves from his father, Nezirus does not apply to him.
Objection: This should also teach that slaves cannot be Nezirim!
THE DISTINCTION BETWEEM ERCHIN AND NEZIRUS
Answer #2 (to question 2:g - Rava): Kusim are included regarding Erchin, but not regarding Nezirus.
(Beraisa): "Bnei Yisrael" - Bnei Yisrael can be Ma'arich (vow to give a person's Erech), but Kusim cannot;
Suggestion: Perhaps one cannot be Ma'arich a Kusi.
Rejection: "A man" (includes Kusim).
Regarding Nezirus, "Bnei Yisrael" excludes Kusim.
Suggestion: Perhaps it excludes them only from bringing Korbanos Nezirus, but "a man" teaches that (Isurim of) Nezirus apply to them!
Rejection: Another verse teaches that they do not bring Korbanos Nezirus.
(Beraisa - R. Yosi ha'Glili): "(A Kusi may offer) an Olah", but not Korbanos Nazir.
Question: Perhaps "Bnei Yisrael" excludes Kusim only from eternal Nezirus, and "a man" teaches that (regular) Nezirus applies to them!
Answer (R. Yochanan): Eternal Nezirus is not written in the Torah. A verse would not come to exclude this.
Question: Perhaps "Bnei Yisrael" teaches only that a Kusi cannot impose Nezirus on his son, and "a man" teaches that Nezirus applies to them!
Answer: R. Yochanan taught that imposing Nezirus on one's son is tradition from Sinai. A verse would not come to exclude this.
Question: Perhaps "Bnei Yisrael" teaches only that a Kusi cannot be Megale'ach (bring Korbanos Nazir, after his father died) from money that his father set aside for his own Gilu'ach, and "a man" teaches that Nezirus applies to them!
Answer: R. Yochanan taught that Gilu'ach with the father's money is a tradition from Sinai. A verse would not come to exclude this.