Bris Milah
Chazal say that the Mitzvah of Milah is equal to all the mitzvos of the Torah combined. The Torah (Bereishis 17:14) specifies the most severe punishment of kares for whoever doesn't perform a Bris Milah. Of all the positive mizvos, only Milah and the korbon pesach are punishable with kares. Kares literally means to be "cut off " or excommunicated from Hashem. This is a form of spiritual death in which the neshomah's connection to Hashem is severed. Kares is considered the most severe of punishments since even a punishment of physical death is an atonement for the neshomah where the neshomah's connection to Hashem is renewed. Since the days of the Roman Empire two thousand years ago until Communist Russia in recent times, Bris Milah has been one of the first Mitzvos to be outlawed when anti-Semitic authorities came to power. Yet, time and time again, Jews have risked their lives to ensure that their children received a kosher Bris Milah.