"I am not what I ought to be, I am not what I want to be, I am not what I hope to be in another world; but still I am not what I once used to be, and by the grace of God I am what I am." - John Newton
John Newton is, quite literally, the wretch the song refers to. A slave trader on The Greyhound, Newton converted in the midst of a storm (though he later admitted "I cannot consider myself to have been a believer, in the full sense of the word.") Many of us know the song, but not many of us know the dark past of the man who wrote it. But what I hope every Christian who reads this does know is that it doesn't matter. Christianity isn't an instant zap into perfection. Newton, following his conversion, gradually grew from ruthless slave trader to an important figure in the abolition movement. Even with slavery in his past, Newton did not immediately become sinless.
Newton is not the first to write about the concept of Christian development. In Philippians, Paul writes that he has not already been perfected, but that he pressed on that he may lay hold of that for which Jesus laid hold of him. As human beings, we were designed for a purpose. We were designed to be good image bearers of God, certainly a goal we ought to strive for. But in this life, striving is all we can do. We are weak in our flesh, and John says that if we say we have no sin, we are deceiving ourselves, and the truth is not in us (1 John 1:8).
This fact is both comforting and discouraging. On the one hand, the knowledge that failure is all but inevitable is rather sad. I don't want to sin anymore, but even if I get rid of the "bigger" sins in my life, I'm still going to slip up. But it's comforting because I know that I have hope. I have hope that all the terrible things in my past are forgiven. I have hope that the terrible things I do now, or the terrible things I will do in the future, are also forgiven. I have hope because God knows I'm going to mess up, and so I can't disappoint Him. But most importantly, I have hope that while I haven't already been perfected, I am heading for perfection. If you're a Christian, so are you! A time will come when God will "hit your re-boot button", making you superior in every conceivable way to Adam and Eve on the day He declared the world "very good".
As John Newton relied on God's grace to make him a better person, so also must you rely on God's grace to make you a better person. You will never be perfect in this life, but you should act as if one day, you will be. Like a child playing Grown Ups, behave as if you are already perfect. As if you have already died, been to Heaven and have been sent down to the Earth as an ambassador.