According to the Bible, the heart is the centre not only of spiritual activity, but of all the operations of human life. "Heart" and "soul" are often used interchangeably (Deuteronomy 6:5; 26:16; Comp. Matthew 22:37; Mark 12:30, 33), but this is not generally the case.

The heart is the "home of the personal life," and hence a man is designated, according to his heart, wise (1 Kings 3:12, etc.), pure (Psalm 24:4; Matthew 5:8, etc.), upright and righteous (Genesis 20:5, 6; Psalm 11:2; 78:72), pious and good (Luke 8:15), etc. In these and such passages the word "soul" could not be substituted for "heart."

The heart is also the seat of the conscience (Romans 2:15). It is naturally wicked (Genesis 8:21), and hence it contaminates the whole life and character (Matthew 12:34; 15:18; Comp. Ecclesiastes 8:11; Psalm 73:7). Hence the heart must be changed, regenerated (Ezek. 36:26; 11:19; Psalm 51:10-14), before a man can willingly obey God.

The process of salvation begins in the heart by the believing reception of the testimony of God, while the rejection of that testimony hardens the heart (Psalm 95:8; Proverbs 28:14; 2 Chronicles 36:13). "Hardness of heart evidences itself by light views of sin; partial acknowledgment and confession of it; pride and conceit; ingratitude; unconcern about the word and ordinances of God; inattention to divine providences; stifling convictions of conscience; shunning reproof; presumption, and general ignorance of divine things."

Noah Webster's New International Dictionary of the English Language

1. (n.) A hollow, muscular organ, which, by contracting rhythmically, keeps up the circulation of the blood.

2. (n.) The seat of the affections or sensibilities, collectively or separately, as love, hate, joy, grief, courage, and the like; rarely, the seat of the understanding or will; -- usually in a good sense, when no epithet is expressed; the better or lovelier part of our nature; the spring of all our actions and purposes; the seat of moral life and character; the moral affections and character itself; the individual disposition and character; as, a good, tender, loving, bad, hard, or selfish heart.

3. (n.) The nearest the middle or center; the part most hidden and within; the inmost or most essential part of any body or system; the source of life and motion in any organization; the chief or vital portion; the center of activity, or of energetic or efficient action; as, the heart of a country, of a tree, etc.

4. (n.) Courage; courageous purpose; spirit.

5. (n.) Vigorous and efficient activity; power of fertile production; condition of the soil, whether good or bad.

6. (n.) That which resembles a heart in shape; especially, a roundish or oval figure or object having an obtuse point at one end, and at the other a corresponding indentation, -- used as a symbol or representative of the heart.

7. (n.) One of a series of playing cards, distinguished by the figure or figures of a heart; as, hearts are trumps.

8. (n.) Vital part; secret meaning; real intention.

9. (n.) A term of affectionate or kindly and familiar address.

10. (v. t.) To give heart to; to hearten; to encourage; to inspirit.

11. (v. i.) To form a compact center or heart; as, a hearting cabbage.