"and he make unclean the head of his Naziritism": Scripture here speaks of one who was clean (when he began his Nazirite count) and became unclean. It is he who must remove his hair and bring an offering, and not one who undertook Naziritism in the cemetery (in which instance he was already unclean.) For it would follow (otherwise), viz.: If one who was clean and became tamei is liable to remove his hair and to bring an offering, how much more so one who was unclean in the beginning!
It is, therefore, written (to negate this) "and he make unclean the head of his Naziritism." "then he shall shave his head": It is his head that he shaves, and not all of his (bodily) hair. For it would follow (otherwise), viz.: Since a leper shaves and brings an offering and a Nazirite shaves and brings an offering, then if I learned of a leper that he shaves all of his hair, then a Nazirite, too, should shave all of his hair. — No, this may be true of a leper, who undergoes a second shaving (Vayikra 14:9), wherefore he shaves all of his hair.
Would you say the same for a Nazirite, who does not shave a second shaving? — wherefore he should not shave all of his hair. — This is refuted by the Levites, who, though they do not undergo a second shaving, shave all of their hair. It must, therefore, be written "then he shall shave his head" — It is his head that he shaves and not all of his hair. ("then he shall shave his head) on the day of his cleansing": on the day of his sprinkling (of the waters of the red heifer [viz. Bamidbar 19:17]).
You say, on the day of his sprinkling, on the seventh, but perhaps ("cleansing" refers to) the day of his offering, on the eighth; it is, therefore, written "on the seventh." If "on the seventh," (I might think that he shaves) even if the waters have not been sprinkled; it is, therefore, written ("then he shall shave") on the day of his cleansing" — the day of his sprinkling, on the seventh. This tells me only of the seventh.
Whence do I derive the eighth, the ninth, and the tenth (as also valid for shaving)? From "he shall shave it" (— in any event). This ("on the day") tells me only of the daytime. Whence do I derive the night (as also valid)?
From "he shall shave it." This tells me only of the shaving for tumah. Whence do I derive (the same for) the shaving of cleanliness (Ibid. 18)? From "he shall shave it." "he shall shave it, and on the eighth day he shall bring, etc." From here (i.e., from the juxtaposition) they ruled: What is the procedure of the shaving for tumah?
First he shaves and then he brings the offering. And if he brought the offering and then shaved, he has not fulfilled his obligation.