"In the moment, Christians should use every possible means to do God’s will. If you feel an impulse to pick up a rock and hurl it at someone — do anything necessary to keep yourself from doing it! Remind yourself, “I’ll go to jail. I’ll disgrace my family!” It would be wrong to give in to the sinful impulse simply because, on the spot, you do not believe the gospel enough to refrain. There is no reason in the short run that a Christian can’t simply use pure willpower if necessary. God deserves our obedience, and we should give it, even if we know our motives are mixed and impure...
Those who say, “We need to put in strenuous effort to obey, even if our belief in the gospel is wanting” are right, at least in the short term. But obedience is not the same thing as change. In the end, all effort is fueled by some motivation, and if our motivation is not the gospel, then we are not obeying God for his own sake neither will we be able to permanently change our character...
In the short run, we should simply obey God because it is his right and due. But in the long run, the ultimate way to shape our lives and escape the deadly influence of our besetting sins is by moving the heart with the gospel."
Tim Keller, Center church