When the Pharisees were scandalized by Jesus' disciples not washing hands before they ate, Jesus called them hypocrites. Then he called the crowd and told them it is not what goes into people's mouth that defiles them, but rather what comes out of it. And finally, when he was left alone with his disciples, he gave a fuller explanation: “Do you not see that whatever goes into the mouth enters the stomach, and goes out into the sewer? But what comes out of the mouth proceeds from the heart, and this is what defiles” (Mt. 15:17–18).

Jesus' argument is based on the fact that in terms of Jewish purity rules, fecal matter may be disgusting but nevertheless it is not ritually unclean. Purity laws are discussed in detail in Leviticus 11–15, and different sorts of bodily uncleanness are enumerated in Leviticus 15. These include flux (flow or discharge), male semen, menstruation, or the spittle (in rabbinical sources also the urine) of someone having a flux, but there is no mention of excrement. In Deuteronomy 23, among other regulations about cleanliness, we read the following passage (Deut. 23:12–14, my italics):