On another forum, I recently posed the question: "As a Christian, do you believe your heart is still 'prone to wander?" -- still in danger of being unfaithful to God, in other words.
"Yes - by experiance I do believe that although I have a new heart, my old man battles against it. Therefore Prone to wander, Lord I feel it, prone to leave the God I love. I believe that it is a constant choice to offer my heart up to God. That HE might take and seal it afresh and anew for the courts above. If my heart was not prone to wander I believe that I would not have to choose this day who to serve."
When God gave you a new heart, why would he give you one that was still prone to wander? Wouldn't that leave us exactly where we were before? It would serve him better to give us a heart that was now steadfast and faithful to him. Otherwise, that "changed heart" or new creation really isn't all that changed.
You might be surprised to learn that it's not your new heart that wanders -- it's your flesh; and in fact Paul says your flesh no longer represents the true you. You can still sin, or course; but your new heart no longer wants to. Your heart/will is already dedicated to His will because Jesus actually replaced that wandering heart with his own heart and purity.
Although your flesh is at war with the Spirit, your heart is not. This actually isn't a new message at all: It's the classic Christian doctrine of "regeneration." In my book, I point out folks from Martin Luther to J.I. Packer who talk about this surprising biblical truth.
We no longer have to daily recommit our heart out of fear that it will wander off. Jesus didn't have to do that. He worshipped God with all his heart certainly, but didn't feel anxious about having to constantly renew his faithfulness to God. His DNA is now in your heart.
[Note: As we talked more, the other person and I seemed to be tracking more together; yet I realized that there's often the acknowledgement of a new heart without understanding the quite radical implications of that new identity. We often want to cling to the dirt in our lives far more than we want to celebrate the radical goodness Jesus has given us.]