On today’s daf, the rabbis grapple with the issue of breaking Shabbat in a moment of necessity. We learn this from a mishnah:
With regard to one who was permitted to leave his Shabbat limit, they said to him along the way: The action has already been performed, and there is no need for you to travel for that purpose, he has 2,000 cubits in each direction from the location where he was standing when this was told to him. If he was within his original limit, it is considered as if he had not left his limit, and he may return to his original location. The Sages formulated a principle: All who go out to battle and save lives may return to their original locations on Shabbat.
This mishnah needs some unpacking. First of all, why was the person permitted to leave the Shabbat limit in the first place?
Rashi explains that the mishnah is talking about someone who was heading out to do a critically important communal service, such as witnessing the new moon or saving someone’s life. It’s easy to understand why it would be permissible for a person to violate the laws of Shabbat to save a life. Jewish law privileges saving a life over almost everything, a principle known as pikuach nefesh. But why would witnessing the new moon excuse straying beyond one’s Shabbat limit?
To understand this, we must remember that the Jewish calendar is lunar. Each new month begins with the new cycle of the moon. While today we have a set calendar, in ancient times, the rabbis relied upon witnesses who saw the new moon to declare the official beginning of a month and determine when various Jewish holidays ought to be observed. Witnessing the new moon was therefore critical to enabling the community to remain united in its observance of the Torah. In that way, establishing the new month maintained communal life just as saving a person maintained human life.
Now, in our mishnah, the Jew on a mission is stopped along the way because the deed they set out to do has already been done. The question is, can that person now go home? It’s one thing to suspend the laws of Shabbat to serve a critical need, but if the need no longer exists, why let the person break Shabbat? The mishnah establishes that the 2,000 cubit distance one is allowed to travel on Shabbat resets when our do-gooder finds out that the mission is no longer necessary. So the person need not wait until after Shabbat to travel home, but can travel 2,000 cubits to get back.
What the rabbis are saying here is that fulfilling a critical communal service is so important that we do not want to make a person think twice about doing so. They don’t want people to refrain from heading out to perform such a service because they’re unsure if the need still exists, or because they might get stuck someplace far from home if it doesn’t. The rabbis did not want anything to get in the way of a person who seeks to serve the community in its hour of need. If you set out on a critical mission, the law will protect you even if you don’t get to fulfill it.