Concise Bible Dictionary:
The heart is often referred to in scripture as the seat of the affections and of the passions, also of wisdom and understanding—hence we read of “the wise in heart,” also the Lord gave to Solomon “a wise and understanding heart.” It is the center of a man’s being. But before the deluge God’s verdict of man was that every imagination of the thoughts of his heart was only evil continually (Gen. 6:5). A similar verdict is found in Genesis 8:21, after Noah came out of the ark. And the Lord said, Out of the heart of man proceed evil thoughts and every form of wickedness (Mark 7:21). The law required man to love God with all his heart. The reception of the gospel must be in the heart, (Rom. 10:9); and God enables a hearer to receive the good news in “an honest and good heart,” upon which there is fruit (Luke 8:15). In new creation there is a “pure heart,” the Christian being led by the Holy Spirit (1 Tim. 1:5; 2 Tim. 2:22; 1 Pet. 1:22).