We all know that we are supposed to be good, supposed to make moral improvement in our lives. We all know that we are not supposed to be immoral wretches who enjoy our wretchedness. But often, I don't think that we really ever stop to ask ourselves "Why?" Why do I want to be good? Why do I want to stop behaving in a particular, sinful way?
What I find is that our motivations are often varied. Sometimes, we want to stop sinning in some fashion because continuing down that road is causing pain in a relationship. So we want to change because we want our friends, spouses, or family members to stop bugging us about this thing we do (or have done, again!). We want peace, so we change. In our better moments, we may even do so in repentant fashion, because we see the hurt we've caused and want to change because we love the person more than we love being the person that we are. Change on these bases is good. It contributes to harmony, and even, at times, personal holiness.
Sometimes we want to change because it will increase our level of social acceptability and help us "fit in." So we stop cussing because that's not cool in our social circles, stop getting drunk because that's frowned upon, and stop running around because that's simply not what nice people do and we want to be viewed as one of the "nice people." And again, that's not worthless change. Who doesn't think that restoring some of our culture's former taboos and recovering the stigma attached to certain behaviors would be a good thing and to the benefit of our culture?
And for me sometimes, I even find that I want to change because I want to be less in need of grace. My theology tells me that I must have grace, because without it, I am completely unacceptable before God. But my pride tells me that needing it is a terrible shame and so I want, sometimes, to change simply so I can feel more worthy and less needy when I come before God.
But the best motivation for change is because we want to glorify God rather than ourselves, please Him rather than our companions, conform to Christ rather than culture, and stand holy before Him because of His grace rather than pridefully working to not need it (an impossible task, since we ar still sinfully prideful). I cannot get out of my head the thought, probably planted there by John Piper or maybe Westminster, that my chief purpose (and yours too) is that we bring glory to God. And He is not glorified by us working harder, but by our allowing His Spirit to transform us, by His grace. He is glorified when we recognize that we need to seek tranformation not so we can feel or look or act better, but because God in Christ has come to save us from our sinfulness so that He can work in us and conform us to the image of the Son and so become, not just better versions of ourselves, but partakers of the divine nature (2 Pet. 1:4). He is glorified when we seek transformation not to better ourselves, but to better glorify Him.