When it’s not permitted to break even the smallest of commadments to save a life
We know that Torah was given to Israel for no other reason than for Israel to live (instead of die) by its commandments. In Leviticus 18:5 we read: “Keep my decrees and laws, for the man who obeys them will live by them. I am the L-rd.” The Jewish sages have long held that to preserve one’s life it is permissible to break any commandment of Torah, except for idolatry (any Chillul Hashem, or the defamation of G-d’s name), sexual sin, and murder. This principal is known as Pikuach nefesh, or preservation of life. If a person’s life or health are in danger, one may break even the Sabbath to help preserve either life or health. If there is no kosher food available and one is starving, a Jew can eat whatever food is available to save his life, even the flesh of swine. If a hemophiliac Jew could die from blood loss, he is permitted to remain uncircumcised. One can break the solemn fast of Yom Kippur if to do so would avoid endangering one’s life or health. There are many other such examples where the preservation of life overrides Torah.
However, there are those times when breaking even the smallest, most seemingly inconsequential of commandments of Torah is forbidden:
When does this rule apply? Not in time of religious persecution. Instead, during the time of religious persecution, a man must be willing to give up his life even for the least demanding of commandments, as is said “You shall not profane My Holy Name – I am to be hallowed among the children of Israel” (Lev. 22:32). (Tos Shab 16:7)