From the words, ovc hju, “and by which he shall live,” Chazal have derived that mitzvos are not to be performed in a way that would endanger someone’s life. Literally, the pasuk is read to mean that mitzvah performance enables one to achieve physical well-being and often longevity. This is in addition to a spiritually healthy moral life replete with the joy and peace of mind inherent when one acts in accordance with the dictates of Hashem. Rashi, however, interprets these words as referring to spiritual longevity in the World to Come, since everyone in this world must eventually die. …
