15 But in your hearts revere Christ as Lord. Always be prepared to give an answer to everyone who asks you to give the reason for the hope that you have. But do this with gentleness and respect, 16 keeping a clear conscience, so that those who speak maliciously against your good behavior in Christ may be ashamed of their slander. — 1 Peter 3:15, 16 NIV
In the Old and New Testament, the word “heart” refers not to the physical organ, but to the center of all of our life processes. The “heart” is the seat of our minds, emotions, and wills. Therefore, it refers to our thought patterns, our attitudes and our desires. Our thoughts become actions which become habits which become our lifestyle. The things and/or people that we spend the most time thinking about, in reality, are the things that control our lives. This is characterized by the following verse:
5 Those who live according to the flesh have their minds set on what the flesh desires; but those who live in accordance with the Spirit have their minds set on what the Spirit desires. — Romans 8:5 NIV