We see in Scripture conflicting opinions about what causes sin, and therefore its remedy. The Jews—the Scribes and Pharisees in particular—viewed sin as being a product of a person’s outward behavior. So they attempted to manage it through a form of law which evolved over time into a system of commandments even stricter than those found in the Law of Moses.
Jesus, on the other hand, knew that sin is primarily a matter of the heart, saying in Matthew 15:19: “For out of the heart come evil thoughts, murders, adulteries, fornications, thefts, false witness, slanders.”
Since most of the sins just listed are acted out by our behavior, it’s not too hard to see them simply as a response by our flesh to some outside stimulus received through our natural senses. In other words: “I wanted it, so I did it!” But in reality, sin manifesting itself through the actions of our body is a symptom of a much more serious disease within.
Sin is a barometer of the heart—a very clear indicator of what is residing within self. Sin is more than just actions; it is rooted in our attitudes, intentions and motives. Given this fact, I find it disturbing (though not surprising) that it’s so common among Christians to ignore the significance of these inner motivations.