What does Proverbs 21:29 mean?

This proverb repeats earlier condemnation of arrogance and unwillingness to learn. The "bold face" noted here is when someone ignores advice or correction, acting as if they are still right (Proverbs 21:24). It can also imply someone using deception and bluster to convince other people of lies. Either way, a godly person is willing to hear advice (Proverbs 12:15), and to change his mind when it's the sensible response (Proverbs 19:20).

Stubbornness is its own form of sinful pride (Proverbs 29:1). Solomon's imagery here is of a person scowling or twisting up their face, like a child who refuses to be told "no." Such a person resists correction. When told to repent and believe, he hardens his heart. He tries to gain others' trust by putting on a hypocritical face that hides his deception. The upright person is more self-reflective, carefully considering what he does. The godly man submits to the Lord. He repents when he is wrong and seeks forgiveness. He relates to others honestly and humbly.

The Pharisees practiced deception. Jesus said they were hypocrites (Matthew 23:13). They appeared to be religious, but they were wolves in sheep's clothing. They appeared to be as clean on the outside, but in their hearts were full of rot and death, like painted tombs (Matthew 23:27–28). At one time the young man Saul of Tarsus was a Pharisee, and he agreed with the murder of Stephen (Acts 7:59—8:1), but the Lord changed Saul's heart, and Saul became a submissive servant of the Lord (Acts 9:1–6).