Rabbinic discipline was built as a ladder, and herem is its top rung. The ordinary instrument was niddui, a temporary separation typically imposed for thirty days: the person under it kept the commandments but was held at arm's length, others keeping four cubits' distance, and the term could be renewed if the offense persisted. Only when repeated niddui failed did the court ascend to herem proper, the full ban: exclusion from the quorum and from the congregation's honors, from commerce and table fellowship, proclaimed publicly and sometimes with the liturgical apparatus of shofar blasts and extinguished candles that made the scene unforgettable. The graded structure matters for what it says about the institution's purpose.
Like its Christian counterpart, the ban aimed at return; the sources discuss its lifting as carefully as its imposition, and a herem could dissolve the day its subject satisfied the court. It was also the tool of a community that governed without a state: medieval kehillot used the threat of herem to enforce taxes, communal ordinances and rabbinic authority itself, because exclusion from the community was, in a hostile wider world, exclusion from almost everything. That very potency argued for restraint, and the responsa literature is full of warnings against cheapening the instrument. With emancipation the ban's force collapsed, a person could simply walk into the surrounding society, and modern Judaism retains herem mostly as history, its ladder a record of how a scattered people disciplined itself for two millennia.