What does the Bible say about the believer's heart?

The believer's heart is crucial in the life of a Christian. It is often described in Scripture as a heart that is whole, broken over sin, willing, and stirred by the Spirit of God. For instance, Psalm 86:11 speaks of a 'united heart' towards God, emphasizing the need for a heart that is wholly devoted. A broken heart, as mentioned in Psalm 51:17, is one that recognizes its brokenness over sin and seeks forgiveness. This transformation of the heart signifies the profound work of God in the believer's life, illustrating that true change comes from Him alone.