What does the Bible say about the condition of the heart?

According to biblical teaching, particularly found in Jeremiah 17:9, 'The heart is deceitful above all things, and desperately wicked: who can know it?' This highlights the radical corruption of the human heart, demonstrating our need for divine intervention. In Joel 2:12-14, we see God's command to 'rend your heart' rather than merely the outward expression through garments. This emphasizes that a true return to God must involve an inward change, necessitating God's grace to grant us a new heart that genuinely seeks Him.