What does the Bible say about hardness of heart?

In Mark 3:1-6, we see Jesus confront the hardness of the Pharisees' hearts. He describes their attitude as grieved and angry because they lacked compassion for a man in need. The hardness of heart is a result of self-righteousness that blinds one to the goodness of mercy and the presence of God. This hardening can stem from a prolonged focus on legalistic religion, diverting attention from the grace of God, which is essential for true worship and service. A heart hardened by legalism cannot see or appreciate the goodness of God in Christ.