Ceremonial defilement prohibited a Jew from approaching a sanctuary or offering sacrifice and forbade human fellowship. It might be contracted by tending a corpse (which accounts for the behaviour of the priest and the Levite in the parable of the Good Samaritan, Luke 10), by ‘leprosy’ (Mark 1: 44), or by menstruation, with the implication of being frequently excluded from society. An elaborate system of rules about defilement existed by the time of Jesus, and he taught that moral duties had priority (Mark 7: 2–4).