Much of today’s daf (Shabbat 132a) is dedicated to identifying a suitable biblical prooftext to support the halacha that a Brit Milah (circumcision) may be performed on Shabbat, and though a number of different prooftexts are analysed, two different prooftexts are ultimately identified in the Gemara (Shabbat 132a) with a further valid prooftext being offered by Rabbi Eliezer in the Mechilta (on Parshat Ki Tissa).
1. According to Rabbi Nachman Bar Yitzchak, the halacha that Brit Milah overrides the laws of Shabbat can be derived from a ‘gezeira shava’ (where the same word of phrase appears in verses relating to Brit Milah and Shabbat respectively). Specifically, because the laws of Brit Milah as presented in Lech Lecha (Bereishit 17:11-12) contain the words of אות (sign), ברית (covenant) and לדורות (for generations), as do the laws of Shabbat as presented in Ki Tissa (Shemot 31:13, 16), we can learn that there is a relationship between Brit Milah and Shabbat and that Brit Milah overrides the laws of Shabbat.
2. According to Rabbi Yochanan, the law that a Brit Milah overrides the laws of Shabbat can be deduced from the word ביום (on that day) which is found in the verses relating to Brit Milah in Parshat Tazria (Vayikra 12:3), as if to teach that a Brit Milah should take place on the eighth day – even if that day is Shabbat.
3. According to Rabbi Eliezer (in the Mechilta), the phrase לעשות את השבת (to do on Shabbat) which features in the verses about Shabbat in Ki Tissa (Shemot 31:16), indicates that there are certain things that can be done on Shabbat, and the later phrase לדורותם ברית עולם (this will be a covenant for all generations) teaches us that the covenant of Brit Milah is among those things that override the laws of Shabbat.
Reflecting on these three teachings, R’ Menachem Mendel Schneersohn zt’’l, known to many simply as the (7th) Lubavitcher Rebbe, notes that it is of significance that each of these prooftexts are sourced from different parts of the Torah (see Likutei Sichot 35, Lech Lecha Sicha 3). According to Rabbi Eliezer, this law is deduced directly from verses about Shabbat. According to Rabbi Yochanan, this law is deduced directly from the verses about Brit Milah. While according to Rabbi Nachman Bar Yitzchak, this law is deduced from a gezeira shava connecting the laws of Shabbat with the story of Avraham who underwent Brit Milah as described in Parshat Lech Lecha.
And why is this significant? As he explains, according to Rabbi Eliezer whose prooftext is from verses about Shabbat, it seems that the Shabbat laws have an in-built exception to allow Brit Milah to be performed on Shabbat. According to Rabbi Yochanan whose prooftext is from verses about Brit Milah, it seems that the mitzvah of Brit Milah has the power to override the laws of Shabbat. While according to Rabbi Nachman Bar Yitzchak whose prooftext is from the story of Avraham which preceded the giving of the Torah and the laws of Shabbat, we learn that the permission to perform a Brit Milah on Shabbat goes beyond the classic categories of Torah law or the laws of Shabbat, because Brit Milah is special as evident from the statement in our Gemara that when Avraham was commanded to undergo a Brit Milah, the word ‘covenant’ was used thirteen times (see Bereishit 17:1-22).
What we learn from here is that while the pursuit to identify a suitable biblical prooftext may seem like a legal technicality, if we pay close attention to these verses and where they come from, we can reveal deeper debates about how halacha operates and how certain mitzvot are afforded both halachic and supra-halachic priority.