What does the Bible teach about the heart of man?

According to Scripture, the heart of man is fundamentally corrupt, as shown in Jeremiah 17:9, which states, 'The heart is deceitful above all things, and desperately wicked: who can know it?' This highlights the intrinsic nature of sin that manifests in thoughts and actions. Jesus reinforces this in Mark 7:20-23, where he teaches that defilement comes from within, identifying thoughts such as evil, deceit, and pride as originating from the heart. Understanding the true condition of the heart emphasizes the need for regeneration, as only God can transform the stony heart into one of flesh that seeks Him.