If our spiritual goal for maturity is to "sin less" then we will be forever frustrated. With a goal of sinning less, then the tendency is to come up with a way to rate our spiritual progress by "obedience to the bible" or "service to others" or "more quiet time" or anything that we think should result in less sin. We then do things that show our maturity, but we end up with a simple immature self-righteousness from the things we "do", and have no power over our sinful nature, and na-da in the "transformation" department. In fact, as over time God puts the spotlight on our real sinful nature, instead of sinning less, we find we are riddled with sin, actually appearing to sin MORE! All we can do then, is to rationalize our view of God down to size, and our view of ourselves UP, with our own self-righteousness, using the very sinful thinking that the gospel has saved us from. It's a "lose-lose" way to "do religion", and that's all it is; religion that even a non-believer can see is no religion at all, as we are just the same old selfish person we always were. We only fool ourselves, and are believing our own lies! That's why they call it denial.
Our goal for maturity has to be gospel transformation - turning from sin, and putting faith in Christ. Repentance and faith. Just like the gospel. The very gospel that saved us eternally, keeps saving us (from ourselves). Sin in itself is rooted in idolatry. At the moment we sin we are seeking to place our trust in something other then Jesus. We need to realize sin is sin, and confess it, but we can't just say to ourselves, "I need to stop this lying, or prideful thinking, or immoral activity." We need to ASK what is inside of me, what idol, that is telling me that I trust it, or need it, more than Jesus. The sin we commit is only the action or reaction that comes from our wrong thinking, and is a separate part, the ill fruit, of our wrong thinking. If we look inside, we find that often the idol behind sin is self centeredness or a desire to be in control. We need to keep asking (Paul reminds us to seek humility) until we see inside of us just what it is that we think (wrongly) is more important to us then trusting in Christ. How often is it just ourselves, our own high regard for us, in the way? Yet even high "self-regard" is often just more sin, just another smoke screen to the real problem. We need to keep asking. Dig deeper still.
The Gospels, especially Mark, are loaded with the command "not to be afraid". We are all riddled with fear deep inside, when we are apart from the Gospel of Jesus. Looking inward and asking "What is our idol?" often reveals that we are going for the "quick fix" to validate ourselves, to get us through our insecurities, our messed up lives, rather then letting the love of God, as given by Jesus on the cross, be our validation. In the gospels Jesus heals, then he says, "Your sins are forgiven." We are all broken inside, wicked and depraved, frightfully fearful, and the more mature a Christian we become, the more we see it, and the more we see our need of HIM to heal us and to validate us by his love, rather than do it ourselves. Only through Christ and his cross are we truly freed from sin. When we see our trust put back in Him, our humble true dependence for our daily bread put on him, then our thinking changes, and only then can our behavior do likewise. By faith in Him, actually trusting Him, we come to realize that he really is changing us, and helping where we can't do it alone. It's a grace by which our only response can be to worship Him with all our hearts, all our might. It's how we can do all things in the name of him who saved us, giving him the glory.
So transformation might be as the nominalist says, "Not that important." Or as the pacifist says, "I need to surrender, just let go, and let God." or the legalist says, "I need to just learn and obey the bible." But all these ways of thought are barriers to transformation, and are the way to self righteousness, not the imputed righteousness of Christ. Paul says put to death the things of the world and put on virtues, seeking humility and love. Wrap ourselves in Christ with our minds on things above. When we imitate Christ, seek his humility, we begin to discover how we need healing inside, and only his love can heal us, and only his gospel forgives us and frees us, and transforms us. Minimizing, surrendering, or obeying are all band-aids on the wrong wound.
So the sign of a mature Christian? An exponentially deepening understanding of how badly we need Christ and forgiveness every day. With this the fruits will come.
Provocations and Pantings has an Aug 30th post on Bob Thune's gospel transformation series for those interested. You will need iTunes to play them. Above is only a very brief summary. Thune, nephew of Senator John Thune of S. Dakota and lead pastor of Coram Deo Church in Omaha, presented this series a few years ago at a college retreat, and it is very easy to understand.