When a husband is not doing a good job of loving his wife, or a wife is not honoring her husband, what needs to happen?
When a guy is struggling to stay away from internet porn, or a girl is trying to stop gossiping about a former friend, what does each one need to do?
Well, of course the answer is "try harder," right? Wrong.
The first thing they need to do is realize the problem is in their heart, not just in their behavior. It's fairly easy to change one's behavior for a little while. The husband can stop by a florist on the way home from work and pick up some flowers. The wife can cook her husband a nice meal. The young man can put an internet filter on his computer. The girl can find a new circle of friends to hang out with. These measures may be good things to do, but they won't solve the problem because they don't address it at the source.
Jesus made it clear that for behavior to improve, the heart must change. It is “out of the overflow of the heart [that] the mouth speaks” (Matthew 12:34b). According to the Bible, the heart is “the wellspring of life” (Proverbs 4:23). It's the origin of the emotions, the will, and the motives and priorities by which one lives. So work on the heart, and you'll eventually get behavior change.
Jesus also used the analogy of fruit trees. He said, "Make a tree good and its fruit will be good, or make a tree bad and its fruit will be bad, for a tree is recognized by its fruit" (Matthew 12:33). In other words, how one habitually behaves indicates whether the heart is healthy. Fix the tree (i.e., the heart) and the fruit (or behavior) will look, taste, and smell better.
The implications of this principle are huge. People come to me all the time looking for the key to a better marriage, or the secret to raising good kids, or victory over temptation, or a way to develop a better attitude about life, or some such thing. These aren't bad things to desire. There are probably some things those people could do to improve their lot in life.
But most of the time, I imagine Jesus would say something like this to us:
"Look deeply into your heart. What's going on down there? Is it fear, or pride, or self-righteousness, or a desire for people's admiration that's at the root of your problem? Is there in your heart a deep-down craving for people to worship you...a lust for control...a secret wish that others suffer instead of you? If so, those are the really ugly things. Repent of those things. Fight against those things. 'Tear your heart, not your clothing' (Joel 2:13). Don't just patch on a few 'action steps' and call it a victory. Dig down deep until you've found the motivating needs underneath your neglect of your spouse, your lust, your gossip, your anger, your forgetfulness. Because if you don't know your heart, and experience heart change, you'll just go right back to that old behavior. Except that you'll be worse off. You'll either fall into despair because you're back in the pits again, or you'll get proud of yourself for learning a new way to act like a Christian."
Heart change is more painful than behavior modification. It takes longer too. But it's the only thing that really transforms lives and marriages and churches and cultures.
It's also something we can't do on our own. God has to help us. He has to lead us on the journey through our heart, show us each pothole and each ugly place, and give us His Spirit of repentance. That's why the psalmist prays, "Create in me a pure heart, O God, and renew a steadfast spirit within me" (Psalm 51:10).