NUM37 Regarding the mitzvah of nazir, [One who becomes a Nazarite (see Bemidbar 6:1-21) must abstain from consuming any grape part or product, from defilement through contact with the dead, and from cutting his hair], we find that the primary concern of one's Nazaritism is lest he drink [wine] and forget the law, [I.e., the Torah and its mitzvos (Sha'arei Teshuvah Hamevo'ar)] or be led astray by a spirit of wantonness. As such, the Torah forbids him "from anything that is produced by the grapevine, [from the seeds to the skin]" (this verse) – – all of this, as a precautionary measure from the drinking of wine. Our Sages, z"l, commented similarly in the Midrash (Shemos Rabbah 16:2). Cf. Mesillas Yesharim, chapter 11.