First, the obvious, this is not about the heart as a vital organ, a muscle that pumps and circulates the blood throughout the body. Neither is this about romance, philosophical, or literary definitions about the heart.
The focus is on what the Bible has to say about the heart. The Bible mentions the human heart almost 300 times. The heart is that spiritual part of us where our emotions and desires dwell.
Before we look at the human heart, we’ll mention that, since God has emotions and desires, He, too, can be said to have a “heart.” We have a heart because God does. David was a man “after God’s own heart” (Acts 13:22). And God blesses His people with leaders who know and follow His heart (1 Samuel 2:35; Jeremiah 3:15).
The human heart, in its natural condition, is evil, treacherous and deceitful. Jeremiah 17:9 says, “The heart is deceitful above all things and beyond cure. Who can understand it?” In other words, the Fall has affected us at the deepest level; our mind, emotions and desires have been tainted by sin—and we are blind to just how pervasive the problem is.
We may not understand our own hearts, but God does. He “knows the secrets of the heart” (Psalm 44:21; see also 1 Corinthians 14:25). Jesus “knew all men, and had no need that anyone should testify of man, for He knew what was in man” (John 2:24-25). Based on His knowledge of the heart, God can judge righteously: “I, the LORD, search the heart, I test the mind, Even to give every man according to his ways, According to the fruit of his doings” (Jeremiah 17:10).
Jesus pointed out the fallen condition of our hearts in Mark 7:21-23: “From within, out of men’s hearts, come evil thoughts, sexual immorality, theft, murder, adultery, greed, malice, deceit, lewdness, envy, slander, arrogance and folly. All these evils come from inside and make a man unclean.” Our biggest problem is not external but internal; all of us have a heart problem.
In order for a person to be saved, then, the heart must be changed. This only happens by the power of God in response to faith. “With the heart one believes unto righteousness” (Romans 10:10). In His grace, God can create a new heart within us (Psalm 51:10; Ezekiel 36:26). He promises to “revive the heart of the contrite ones” (Isaiah 57:15).
God’s work of creating a new heart within us involves testing our hearts (Psalm 17:3; Deuteronomy 8:2) and filling our hearts with new ideas, new wisdom, and new desires (Nehemiah 7:5; 1 Kings 10:24; 2 Corinthians 8:16).
The heart is the core of our being, and the Bible sets high importance on keeping our hearts pure:
“Above all else, guard your heart, for it is the wellspring of life” (Proverbs 4:23).