The avoidance of ritual contamination. Important to the Hebrews, for impurity effectively prevented much religious and social activity. Impurity could be ‘caught’ by contact with the dead, from prohibited foods, from contact with bodily fluids (e.g. Lam. 1: 9) and various diseases. Leviticus and Numbers describe the laws regarding purity, and the Dead Sea scrolls contain regulations which were designed to maintain within the community a rigorous standard of ritual purity. The purpose of purity regulations is to guard the group against what seems alien and to reinforce the sense of being the chosen people of God, as well as to establish moral purity.
In Christian theology the Jewish laws on purity have been abrogated and their requirements of moral purity strengthened. Jesus had argued that some prohibitions and laws could be overridden in the light of moral insight (Mark 7: 12). But it is unlikely that he swept aside the whole Jewish system. The words ascribed to him in Mark 7: 19 surely come from Mark rather than from Jesus; if this principle had been known when Paul was battling on behalf of ‘his gospel’ (Gal. 1: 8), he had only to appeal to it to settle the controversy.