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

Jeremiah 17:9 emphasizes that the heart is deceitful above all things and desperately wicked, highlighting the depth of human sinfulness. This scripture underscores the inherent corruption of humanity, indicating that our hearts mislead us and lead us away from God. The deceitfulness of the heart prevents us from recognizing our true state before God, making it crucial for believers to rely on divine revelation and not solely on their feelings or intuition, which can be misleading. The passage serves as a sober reminder of the need for God's grace and mercy to genuinely understand ourselves and our relationship with Him.