What does the Bible say about a closed heart?

In the Bible, particularly in Jeremiah 17:9, it is stated that the heart is deceitful above all things and desperately wicked. Before God intervenes, our hearts are closed to the truth of the gospel, unable to receive and believe in God’s word. This state is reflective of being spiritually dead, where one cannot comprehend or appreciate the beauty of Christ or the gospel until God opens their heart. The example of Lydia in Acts 16 illustrates how God actively opens hearts to receive the truth.