The Torah commands: "And the children of Israel shall keep the Sabbath, to observe the Sabbath for their generations" (Exodus 31:16). The Mekhilta DeRabbi Yishmael connects this verse to a teaching by Rabbi Nathan that became one of the most consequential principles in all of Jewish law.
Rabbi Nathan says: "Profane for him one Sabbath so that he will keep many Sabbaths." The principle is startling in its clarity. If a person's life is in danger, you must violate the Sabbath to save them. Not "you may" — you must. The Torah commands Sabbath observance "for their generations," and a dead person has no future generations. Saving a life now ensures that person will observe many Sabbaths in the years to come.
This teaching became the foundation of the rabbinic principle known as pikuach nefesh — the preservation of human life overrides virtually every other commandment. A doctor must treat a critically ill patient on Shabbat (the Sabbath). A person trapped under rubble must be rescued even if it means digging, carrying, and performing every category of prohibited labor.
What makes Rabbi Nathan's formulation so powerful is its logic. He does not argue that saving a life is an exception to the Sabbath. He argues that saving a life is the fulfillment of the Sabbath's own purpose. The Sabbath exists "for their generations" — for the ongoing life of the people. Letting someone die in order to keep the Sabbath would contradict the Sabbath's own reason for being. One violation now purchases a lifetime of sacred observance.