Dear Rabbi Kornfeld:
On the top of daf 68 amud beis; Rebbi Shimon announced (regarding chalavim of the Pesach) - "come and see how precious is a mitzvah in its right time!"
What is the p'shat here? We know that 'mitvas aseh doche mitzvas lo
ta'aseh', but they must occur simultaineously for the rule to be operative.
Here, it's perfectly permissable to burn the chalavim the entire night
(motzei Shabbos), and yet they didn't wait, but rather burned the chalavim *on* Shabbos.
Someone in the shi'ur wanted to say that to do mitzvos "b'sha'atan" is a *separate* (and additional) mitzvas aseh, but it seemed to me that saying that would create all sorts of problems elsewhere.
Can you explain how did this idea of "chavivia" works regarding the burning of these chalavim?
RASHI (DH Kesheirin) explains that this Halachah of burning the Chalavim on Shabbos itself and not waiting until the night is learned from the verse, "Olas Shabbas b'Shabbato," which teaches that the Korban of Shabbos is brought on Shabbos, including all parts of the Korban, even the fats which could be brought Motza'ei Shabbos. (That is, it would have been possible to burn the fats of the Korban at night, but the Gezeiras ha'Kasuv states that it is Docheh Shabbos.) Thus, it is a Gezeiras ha'Kasuv (and not merely a Sevara) that the "Chavivus" of a Mitzvah in its proper time is Docheh Shabbos.
The source for Rashi's words is the Gemara in Shabbos (133a). The Gemara there says that even though the rule of "Aseh Docheh Lo Ta'aseh" does not apply when it is possible to fulfill both, nevertheless a Mitzvah in its proper time is Docheh a Lo Ta'aseh (even though it could be done at a less preferable time without coming into conflict with the Lo Ta'aseh). For this reason, the Mitzvah of Milah is *not* Docheh Yom Tov when it is not being done during its proper time (on the eighth day) (according to the opinion that says that Yom Tov is only a Lo Ta'aseh, and not both an Aseh and a Lo Ta'aseh), although it is Docheh Yom Tov on the eighth day (and we don't push it off to the ninth).
We find a similar situation in the case of doing Yibum with a woman who is a Mamzeres. Even though it is possible for the brother-in-law to perform Chalitzah and not to marry the Mamzeres, nevertheless the Mitzvah to marry her and perform Yibum overrides the Lo Ta'aseh of marrying a Mamzeres (at least mid'Oraisa), because "Chalitzah in the place of Yibum is not a Mitzvah," i.e. it is not as big a Mitzvah (Yevamos 20b).