What does Proverbs 30:12 mean?

Several lessons in this passage begin with the translated phrase "there are those." This can also be translated as "there is a generation," and comes from a single Hebrew word. This may have meant the people Agur (Proverbs 30:1) saw in his culture, or mankind at large.

Self-righteous individuals think they are morally and spiritually clean. Yet their self-centered, pretentious attitude makes them filthy in God's sight. The Israelites in Isaiah's day thought adherence to religious ceremonies and sacrifices made them acceptable to God, but they were mistaken. God said they were sinful and loaded down with iniquity (Isaiah 1:4). He commanded: "Wash yourselves; make yourselves clean; remove the evil of your deeds from before my eyes; cease to do evil, learn to do good; seek justice, correct oppression; bring justice to the fatherless, plead the widow's cause" (Isaiah 1:16–17). He issued an invitation to reasonable thought and repentance (Isaiah 1:18).

The Pharisees in Jesus' day are perhaps the most famous example of self-righteous individuals unwashed from their spiritual filth. Jesus compared them to graves painted on the outside but filled with rot and death (Matthew 23:27). He compared their outward façade to their real hearts, marked by hypocrisy and rebellion against God (Matthew 23:28).