This Gemara is difficult to understand. Why should one's personal Korban
override the Mitzvah of "Hashlamah?" Even though it will enable him to
partake of the Korban Pesach, that Mitzvah will not be done until later. We
know that in order for one Mitzvah to be Docheh another one, they must be
done at the same time! Since he will not be doing the Mitzvah of eating the
Korban Pesach until after nightfall, why should he be allowed to forego the
Mitzvah of "Hashlamah" and bring his private Korban for Kaparah after the
Korban Tamid?
(a) TOSFOS (DH Asi) answers in the name of the RIVA that the Gemara is
talking about a case when the person who is Mechusar Kipurim already brought
the Korban Pesach before he brought his Korban for Kaparah. Since he is not
fit to eat the Korban Pesach in his present state, it is not considered as
though he brought it. At the very moment that he slaughters his own Korban
he becomes fit to eat the Korban Pesach and he fulfills the Mitzvah of
bringing the Korban Pesach. That is, at the moment he becomes fit to eat the
Pesach, he is Yotzei the Mitzvah of offering up the Korban. As the Gemara
says later (90a), he is exempt from brining a Korban on Pesach Sheni as long
as he was fit to eat the Korban Pesach on Pesach Rishon. Even though he is
not actually fulfilling the Mitzvah of *eating* the Pesach (which is the
Mitzvah which is punishable with Kares), nevertheless the Mitzvah of
*bringing* the Korban Pesach is considered to be a weightier Mitzvah that
the Mitzvas Aseh of "Hashlamah," since it is associated with the Mitzvah of
eating the Pesach which does have Kares.
(b) The RI cited by Tosfos answers that in order for one Mitzvas Aseh to
override a weaker Mitzvas Aseh, the two acts do not have to be done at the
same time. Only when one wants to be Docheh a Lo Ta'aseh -- which is a
stronger Aveirah -- with an Aseh do they then have to be done at the same
time.
RAV YISRAEL ZEV GUSTMAN, zt'l, used to explain that the underpinnings of
this question may be based on a broader question. Why is an Aseh able to be
Docheh a Lo Ta'aseh? After all, a Lo Ta'aseh -- an Isur -- is more severe
than an Aseh (Yevamos 8a). There are two approaches to this question in the
Rishonim.
RABEINU NISIM GAON in Shabbos (133a, see Insights there) explains that the
Aseh is not really "*Docheh*" the Lo Ta'aseh. The Aseh does not push away or
override the Lo Ta'aseh. Rather, in situations where the Lo Ta'aseh comes in
conflict with an Aseh, the Lo Ta'aseh was never commanded in the first
place! That is, the Torah did not give the commandment to observe the Lo
Ta'aseh when it is in conflict with an Aseh. The Lo Ta'aseh is in force
contingent upon there being no Aseh opposing it. If there is an Aseh
opposing it, then the prohibition of the Lo Ta'aseh was never said in the
first place.
If so, the condition that the Aseh and Lo Ta'aseh have to be done at the
same time in order for the Aseh to be "Docheh" the Lo Ta'aseh is actually
describing the condition under which the Lo Ta'aseh was commanded. That is,
when did the Torah not command the Lo Ta'aseh when it clashes with an Aseh
-- only when the Lo Ta'aseh is in opposition to an Aseh at the very same
time that the Aseh is being performed. But when they are not being done at
the same time, the Lo Ta'aseh *does* take effect and it remains in force
because it is stronger than the Aseh which cannot override it.
This is the opinion of the RI here. The Ri explains , and that is why he
explains that a strong aseh being docheh a lo taaseh, logically one is
stronger than the other, and therefore you don't need this clause that when
they come into opposition the torah never gave one. It is mdechiyah and not
mdin hutrah. Therefore even not idnei it can be docheh.
The RIVA, on the other hand, learns that every case of "Aseh Docheh Lo
Ta'aseh" works by pushing aside the Lo Ta'aseh ("Dechiyah"), and not the way
Rabeinu Nisim Gaon explains ("Hutrah"). He learns that an Aseh is stronger
than a Lo Ta'aseh (see Ramban to Shemos 20:8), as the MAHARIK (Shoresh 139)
writes. The rule that the Aseh must be done at the same time as the Lo
Ta'aseh is merely in order to ensure that the person not do the Aveirah
first and then forget about doing the Mitzvas Aseh. This will apply equally
when one Aseh is Docheh a weaker Aseh.
The Riva seems to be consistent with his opinion elsewhere (Tosfos, Chulin
141a), where he writes that when an Aseh is opposed by another Aseh and a Lo
Ta'aseh, one is not permitted to perform the Aseh by transgressing the other
Aseh and the Lo Ta'aseh. However, if one, b'Di'eved, transgressed and
performed the Aseh, he does not get Malkus for transgressing the Lo Ta'aseh,
because the fulfillment of the Aseh is Docheh the Malkus (see Insights,
Pesachim 47b). This makes sense according to the Riva's opinion that the
Aseh is stronger than the Lo Ta'aseh and therefore it is Docheh it, as the
Maharik (ibid.) points out. According to Rabeinu Nisim Gaon, on the other
hand, the Torah *did* command the Lo Ta'aseh in such a situation, so it will
not be pushed aside at all and one will receive Malkus.