The Rishonim ask how could it suffice to count the last ten days for his own
Nezirus? If he shaved after observing his son's Nezirus, then he only has a
ten-day hair-growth on his head, and thus instead of observing ten days, he
should have to observe thirty full days of Nezirus in order to grow his hair
long again!
(a) TOSFOS explains that at the conclusion of the Nezirus for his son, he
simply does not shave or bring the Korbanos of his Nezirus. Instead, he
shaves ten days later after he finishes his own Nezirus, and at that time he
brings both sets of Korbanos -- for his son's Nezirus and for his own
Nezirus. Even though he is required to put all of his hair in the fire
underneath the pot in which his Korban Shelamim is cooking, and here there
are *two* Korbanos Shelamim, he could put both Korbanos in a single pot and
then put the hair underneath that pot.
We might ask, though, is there no problem in a Nazir delaying the shaving
and the Korbanos of his Nezirus (in this case, of the Nezirus for his son)?
What about the Isur of Bal Te'acher, that a person is not supposed to delay
bringing his Korbanos? The answer is that this is not a problem. The Gemara
in Rosh Hashanah (6a) says that the Lav of Bal Te'acher only applies when a
person delays bringing his Korban past three Regalim, and the Isur Aseh of
delaying a Korban applies only when he delays it past the nearest Regel. But
if he delays for just a few days, before the next Regel arrives, there is
nothing wrong.
(b) The ROSH suggests that perhaps the Nazir *does* shave after he finishes
his son's Nezirus. When the Mishnah says that he only finishes ten more days
for his own Nezirus, it means that he counts ten days of his Nezirus and
then another twenty days of "Gidul Se'ar," of growing his hair; these days
are not considered part of his actual Nezirus. A Halachic difference between
days of "Gidul Se'ar" and days of Nezirus would be if he becomes Tamei
during the days of "Gidul Se'ar," it will not annul the days of Nezirus that
he already counted, since only becoming Tamei during days of *Nezirus*
annuls the days that he observed, like Rav says (14b). (Shmuel argues and
says that Tum'ah annuls the days of his Nezirus even during the days of
"Gidul Se'ar." The Rosh suggests other practical differences that apply even
according to Shmuel.)
Why does the Rosh insist that the Nazir shaves his hair at the conclusion of
his son's Nezirus? If, by shaving his hair, he will have to observe another
twenty days of hair growing, then why does he not just delay his Korbanos
until his own Nezirus is over (in ten more days), like Tosfos explains?
It seems that the Rosh learns that if he does not shave after his son's
Nezirus, he cannot return to count his own Nezirus. There must be an *act*
of shaving and bringing Korbanos that denotes the conclusion of one Nezirus,
separating his son's Nezirus from his own. Hence, if he would delay his
haircut for another ten days, he would still need to observe another thirty
days for his own Nezirus after cutting his hair for his son's Nezirus.
Perhaps a source for this view of the Rosh can be found in the Mishnah
earlier (8a). The Mishnah states that if a person accepts upon himself to
become a Nazir as many times "as there are heads on his head," he becomes a
Nazir forever, constantly renewing his Nezirus, and he shaves every thirty
days. The ROSH there questions whether the Nazir must shave every thirty
days, or whether he may delay shaving until the festival (and bring only one
set of Korbanos then), since he does not transgress Bal Te'acher until the
festival passes. The Rosh there concludes that it seems most logical that he
must actually end each Nezirus after thirty days and bring Korbanos for each
Nezirus. Since the person accepted upon himself to observe an unlimited
number of Nezirus periods, he has to fit in as many Nezirus periods in his
life as he can. Otherwise, he is pushing off the fulfillment of his vow.
This seems to be the intention of the Mishnah that writes that "he shaves
every thirty days," rather than saying that he shaves every festival. If,
however, a second Nezirus could start before he shaves for the first
Nezirus, then why should it be necessary for him to shave and bring Korbanos
to the Beis ha'Mikdash every thirty days? He should wait until the festival,
and every thirty days the Nezirus will automatically re-start (even though
he did not bring Korbanos), and on the festival he could bring many sets of
Korbanos for every thirty days that passed. Why does the Mishnah write that
he shaves every thirty days, instead of saying that he starts a new Nezirus
every thirty days, or that he brings, at the time of the festival, a set of
Korbanos for every thirty days of Nezirus that he observed? This implies
that shaving is necessary in order to end one Nezirus and begin the next
one. This is why the Rosh writes that he must shave immediately after
observing his son's Nezirus before observing his own Nezirus.
A more obvious source for the Rosh's view might be the opinion of the
Chachamim (18b) who say that a Nazir Tamei may not begin his Nezirus Taharah
until after he brings his Korbanos for the Tum'ah. Even though Rebbi Eliezer
argues and says that he starts the Nezirus Taharah before bringing the
Korbanos for his Tum'ah, the Halachah follows the view of the Chachamim.