Frontlets, or phylacteries, were leather cases containing written passages from the Law. They were worn on the left arm and forehead, with the forehead case divided into cells for separate parchment strips.
Jesus criticized the Pharisees for making their phylacteries broad and conspicuous. The criticism concerned their outward religious display and pretentious customs rather than merely the prescribed existence of the phylacteries.
The cases were made of black calfskin and attached with leather thongs. The written passages were from Exodus and Deuteronomy. The phylacteries were used as amulets; Pharisees reportedly wore them continually, while ordinary people used them chiefly at prayer.