If one experiences a life-threatening situation or illness, there is a Torah obligation to desecrate the Shabbat on his behalf, for instance, by rushing him to the hospital by car; indeed, there is a Mitzvah to perform any other forbidden work on Shabbat that is necessary to save the individual’s life.
Shabbat is completely pushed aside when it comes to saving a life, as Shabbat is included in all other Mitzvot regarding which the Torah exclaims, “And you shall keep all my laws which man shall perform ‘and live through them,’” and not that he should die as a result of them. This rule excludes the three cardinal sins for which one must indeed forfeit one’s life so as not to transgress them, which are: adultery, idolatry, and murder.
The general rule is: Concerning a person suffering from a life-threatening ailment or situation, Shabbat is like a regular weekday regarding all the things he is in need of. It is prohibited to delay desecrating the Shabbat for a person whose life is in danger, for the laws of the Torah are completely merciful, kind, and peaceful. The Karraites denied belief of the Oral Torah and would say that it is prohibited to desecrate Shabbat for one whose life is in danger; about them does the verse state, “And I have also given them laws which are not good and tenets by which they shall not live.” The quicker a person is to desecrate Shabbat in a life-threatening situation, the more praiseworthy he is.
The Talmud Yerushalmi states that the quicker one is to desecrate Shabbat in a life-threatening situation, the more praiseworthy he is, and if one goes to ask a Torah scholar if he may desecrate Shabbat in a life-threatening situation, it is tantamount to him spilling blood, for during the time he delays desecrating Shabbat, the patient is coming closer and closer to the brink of death.
The Ramban writes in his Sefer Milchemet Hashem: “There is no measure of piety regarding a person whose life is in danger and acts stringently by having others not desecrate Shabbat on his behalf; on the contrary, whoever does so in a life-threatening situation is held accountable for his own life, as the verse states (regarding one who commits suicide), ‘However, I shall seek out your blood from your souls,’ which means ‘From your own souls shall I seek your blood.’”
In Hebrew, a life-threatening situation is referred to as, “Pikuach Nefesh,” which is a term borrowed from the Gemara (Yoma 84a) regarding a situation where a structure falls on a person on Shabbat, we must clear away the rubble (“Mefakchin”) in order to extricate him. Nevertheless, this is obviously not the only action which is permissible; rather, any action necessary to save the life of one who is in danger of death is permissible on Shabbat.