Why does the Torah insert the words "Vechiper alav ... "?
What sin did the Nazir commit?
Rashi #1, Targum Onkelos and Targum Yonasan: He was not careful not to become Tamei.
Nedarim, 10a: The early Chasidim who wanted to donate an Olah or a Shelamim would do so - they would not however, become Nezirim in order to bring it, since the Torah refers to a Nazir as a sinner. 3
Da'as Zekeinim: As if the Torah had written "ve'Lo Yachati" (he distanced his Nefesh from wine). Refer also to 6:11:151:1.
Nedarim, 10a: And if someone who desists from wine is called a sinner, how much more so someone who desists from all food (by fasting). See Torah Temimah, note 84, who elaborates, and to 6:5:1:2*.
Those Chasidim followed the opinin of R. Elzazar ha'Kapar. See answer #2.
What does the Torah mean when it writes "ve'Kidash es Rosho"?
Rashi: It means that he is obligated to begin his Nezirus all over again.
What are the implications of the words "Ve'kadash es Rosho ba'Yom ha'Hu"?
QUESTIONS ON RASHI
Rashi writes that R. Elazar ha'Kapar holds that a Nazir's sin is that he abstained from wine. Then why does a Nazir Tahor not bring a Korban?
Moshav Zekeinim: Because, as opposed to a Nazir Tamei, whose first days are lost and only the Aveirah remains, by a Zazir Tahor, the Mitzvah overrides the Aveirah and a Korban is not necessary 1
Oznayim la'Torah: Because if he became Tamei, it is a sign that he has not yet abandoned his thoughts of pleasure in this world cmpletely, which is not the case by a Nazir who did not become Tamei.
Nevertheless, because the Torah refers to a Nazir as a sinner, R. Shimon in Nedarim, 10a, maintains that the early Chasidim would desist from becoming Nezirim. See Torah Temimah, note 84.