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" 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.