How do we know that salvation is a work of the heart?

The heart in biblical terms encompasses our intellect, will, emotions, and understanding. When David proclaims in Psalm 57 that his heart is fixed, he indicates that genuine faith and salvation begin deep within. Romans 10:10 also teaches that with the heart man believes, leading to righteousness. This transformation results in a new heart that loves God and trusts in His promises, signifying that salvation is not just a change of mind but a profound internal change enabled by God's grace.