Jesus illustrates his point with a vice list, a standard literary form in both Jewish (for example, Wisdom 14:25-26; 1QS 4.9-11) and broader Greco-Roman (for example, Arist. E.E. 2.3.4, 1220b-21; V.V. 1249-51b) circles.

Not food that enters the mouth (Ezek 4:14-15; Acts 10:11-16; Rom 14:1-4; 1 Tim 4:3) but what comes forth (Mt 12:34-37; Eph 4:29; Jas 1:19) renders a person unclean. Alluding to the Isaiah passage he has quoted (Is 29:13; compare 59:13), Jesus emphasizes the heart (compare Mt 5:21-6:18), as did some of his contemporaries (m. 'Abot 2:9). The Pharisees of Jesus' day would have agreed with his emphasis on inwardness, although not that the outward did not defile.

In a church I know well, a deacon I respect in most other matters rebuked a person for wearing work clothes to church (even though she had just gotten off work); another leader in the same church had gone unrebuked for sleeping with a woman to whom he was not married. Many of us modern Christians have a lot of nerve to compare ourselves favorably with the Pharisees!