Office of a spiritual leader expert in the ceremonies of worship and the performance of religious rituals. Though chieftains, kings, and heads of households have sometimes performed priestly functions, in most civilizations the priesthood is a specialized office. The priest's duties are concerned less with magic than with the right performance of ritual acts required by the divine powers. Many African societies, for example, differentiated between shamans and the priests responsible for the worship of tribal ancestors. Sacrifice is often one of the most important duties of the priesthood. Not every highly developed religion possesses a priesthood, the most notable exception being Islam. The idea of the priesthood of all believers was also a cardinal doctrine of the Reformation, and the Protestant belief that priests are not needed as intermediaries between church members and the Holy Spirit is seen most clearly in sects such as the Society of Friends.