Hastings' Dictionary of the Bible (1898)
HEART, Acts 16:14. The seat of the affections, desires, hopes, and motives. John 14:1; Esth 1:10. The term is also used by the Bible writers to designate the understanding, 1 Cor 2:9, and intellectual perceptions. It is further a general term for the spiritual nature of man. Isa 1:5; 2 Cor 4:6. In the latter passage the apostle speaks of the light shining in our hearts, teaching us of Christ as the One who reveals God. The heart is declared to be corrupt and full of evil, Eccl 9:3, and deceit, Jer 17:9, the seat of sin and crime. Matt 15:19, as also of faith. Rom 10:10.
The Lord "looketh on the heart," 1 Sam 16:7, in contrast to the outward appearance, and we are commanded to cultivate it, as the most important part of our nature, rather than external appearances. Prov 4:4; Joel 2:13.