The Bible uses the term “heart” to describe the bundle of desires, hopes, interests, ambitions, dreams, and affections you have. Your heart represents the source of all your motivations—what you love to do and what you care about most. Even today we still use the word in this way when we say, “I love you with all my heart.”
The Bible says, “As a face is reflected in water, so the heart reflects the person.” Your heart reveals the real you—what you truly are, not what others think you are or what circumstances force you to be. Your heart determines why you say the things you do, why you feel the way you do, and why you act the way you do.
In the same way, God has given each of us a unique emotional “heartbeat” that races when we think about the subjects, activities, or circumstances that interest us. We instinctively care about some things and not about others. These are clues as to where you should be serving.
(The Purpose Driven Life, By Rick Warren)