Penitential

A penitential is a book or set of church rules concerning the Christian sacrament of penance, used for regular private confession with a confessor-priest, a "new manner of reconciliation with God"^[1] that was promoted by Celtic monks in Ireland in the sixth century AD, under the Egyptian monastic influence of St John Cassian. It consisted of a list of sins and the appropriate penances prescribed for them, and served as a type of manual for confessors.