Moses and Aaron were instructed to be careful with the job specification of the Kohatites. Otherwise these members of the tribe of Levi would find themselves “cut off” (Num. 4:17-18).
The punishment of being “cut off”, karet, is frequently referred to in the Torah. Often we are told that someone who commits a serious transgression would have their soul “cut off from amongst its people”. If an Israelite eats chametz on Pesach, for instance, “that soul shall be cut off from Israel” (Ex. 12:15).
The English translation of karet is usually “extirpation”, but that in itself tells us very little. All the sources agree that it is a punishment that comes from God for a deliberate offence (since it is a punishment from Heaven, karet can not be understood, despite some translations, as excommunication, in the popular sense of that word). It applies to 36 types of transgression listed in the Torah (Mishnah K’ritot 1:1).
There is halachic debate about whether a person deserving of karet can also be punished by a human law court, and whether the court’s punishment now exempts a wrongdoer from karet (Makkot 13a/b, 23a/b).
But what is the nature of karet?
The leading view is that it means premature death, commonly understood as death before the age of 60. Often, as in the Yom Kippur confessions, karet is listed with ariri, childlessness.
But no-one should jump to conclusions. It does not necessarily follow that someone who dies before 60, or a person who has no children, has committed one of the 36 offences listed as deserving of karet. Suffering is not necessarily because of sin.
But on the other hand, are there not people who sin and do not seem to suffer? Where is their karet?
Maimonides answers that a serious sinner who has not repented is indeed punished, by being denied life in the World to Come – i.e. for them, this life is all there is, and they are cut off from any chance of an afterlife (Hilchot T’shuvah 8:1).