Although earlier (see daf 82) the Gemara took for granted that all mitzvot are “pushed aside” in the face of the overarching value of human life (with the exception of avodah zara, gilui arayot and shefikhut damim – idol worship, forbidden sexual relations and murder) the Gemara on our daf presents a question: how do we know that piku’ah nefesh – danger to life – pushes aside the restrictions of Shabbat? Apparently the question here is a more difficult one because it involves not only a person saving his own life, but a source allowing others to desecrate Shabbat in order to save him, as well.
Several sources are suggested by the tannaim and amoraim. For example, Rabbi Elazar ben Azarya finds a source in the mitzva of brit milah – circumcision – which is performed on Shabbat even though it involves activities that are forbidden on Shabbat. Rabbeinu Hananel explains this derivation by pointing out that someone who does not have a brit is liable for the punishment of karet – of being “cut off” from the Jewish people – which is considered the equivalent of death. Thus we find that to “save” the baby from possible karet we can perform the brit on Shabbat, similarly to save a life we can do the same. Rabbeinu Hananel also points out that Moshe was threatened with death when he did not circumcise his son (see Shemot 4:24 ), which is yet another indication of the importance of this mitzva, which, itself, pushes aside any Shabbat prohibitions.
Rabbi Shimon ben Menasya said: It is stated: “And the children of Israel shall keep Shabbat, to observe Shabbat” (Shemot 31:16). The Torah said: Desecrate one Shabbat on his behalf so he will observe many Shabbatot.
Maharil Habib in his Tosafot Yom haKippurim points out that what we derive from this pasuk is the concept that we can “desecrate” Shabbat if the purpose is to fulfill commandments – even if we do not have a guarantee that the person will be able to keep many Shabbatot – since we rule that a person can be mehalel (transgress) Shabbat even to extend another person’s life for a brief period of time.
Perhaps the best known source is the suggestion made by Rabbi Yehuda in the name of Shmuel, who quotes the pasuk (Vayikra 18:5) “…and you should live by them” meaning that the mitzvot are given to the Jewish people to live by, and not to lead them to death. As the Gemara points out, this source includes not only situations in which we are certain that someone’s life is in danger, but even cases where we are not sure whether there is danger to life. The Torah commands that we cannot allow someone to die because of the mitzvot of the Torah.