It's common enough when we encounter someone who's a little rough around the edges to hear one of their defenders say, "But they have a good heart." Indeed, that seems to be how we excuse wrongdoing these days: What we do outwardly is an anomaly; on the inside, where it supposedly counts, we are good people.
Nothing could be further from the truth, of course. If one tenth of the sin we entertain in our hearts were to be acted upon, the population of the world would probably be in prison. In Matthew 15, Jesus tells the religious authorities that what we put into our mouths doesn't defile. It's what comes from our hearts that defiles.
I need, therefore, to stop pretending that the wrong I do isn't reflected in my heart, which is basically good. For my actions wouldn't occur without my mind. And my mind wouldn't be corrupt if it weren't for my inner being which gives rise to the thoughts I entertain. It doesn't matter if I attempt (or pray for) change in my actions, for my secret heart will still remain unreformed.
Change me, Lord, not on the outside, but on the inside. Only then will my actions match what I say I believe. Amen.