To illustrate our need for a changed heart in addition to changed behavior, author Christopher Ash uses the following illustration (or object lesson) based on David's sin with Bathsheba:

Suppose I hold a glass of water and I shake it. Water spills out, and you ask me, "Why did water spill out?" The instinctive answer is, "Water came out because you shook it." But there is another correct answer, which is, "Water came out because water is what was inside the glass. If there hadn't been water in the glass in the first place, no water would have ever come out of the glass." Sure, it came out because it was shaken, but water came out because water was inside.

So if we asked David, "Why did you do what you did?" He might say, "I did it because I was tempted, because of pressure. I was, as it were, shaken. My equilibrium was disturbed by outside influences, things that happened to me. I was weary. I looked out of the window and saw this beautiful woman, and one thing led to another. I was shaken." That's what we instinctively say. "I said that because I was stressed." "I did that because I was tired, or sick." "My upbringing has conditioned me to react that way."

But David's answer [see Psalm 51] is, "I committed adultery because there is adultery in my heart": "I covered up because there is pride in my heart"; "I murdered because love of self and hatred of others is in my heart." The really shocking thing I have discovered, says David, is that what I did expressed who I am. Evil came out of me because there is evil in me.