What does Mark 7:20 mean?

cleanness and uncleanness are priorities (Leviticus 10:10), but they aren't necessarily determined by sin. Disposing of something or someone that is dead makes someone unclean (Leviticus 5:2). A dead mouse lying on a piece of cloth makes the fabric unclean (Leviticus 11:29–32). Childbirth (Leviticus 12:2), having sex (Leviticus 15:16–18), and menstruation (Leviticus 15:19–24) make people and sometimes the things the people touch unclean. Even a skin condition makes someone unclean (Leviticus 13:35–59) and mildew on a house makes the house unclean (Leviticus 14:33–53).

This is the type of "uncleanness" the scribes and Pharisees wish to avoid. While at the marketplace, they have no way of knowing if the vender picked up a dead mouse or if a locust fell into the basket that holds the grain. By washing, they hope to cleanse themselves and their food so they will not become unclean unintentionally.

Jesus' concern, however, is that as the religious leaders teach about ceremonial uncleanness, their hearts are black with sin: the scribes and Pharisees emphasize keeping an oath over caring for one's parents (Mark 7:9–13). God has no use for teachers who go above and beyond in their religious service but treat people with callousness. Matthew 15:18 specifically says, "But what comes out of the mouth proceeds from the heart, and this defiles a person." The traditions we observe mean nothing if our hearts are hard.