You are not your sin; sin is no longer the truest thing about the man who has come into union with Jesus. Your heart is good. "I will give you a new heart and put a new spirit in you" (Ezek. 36:26). The Big Lie in the church today is that you are nothing more than "a sinner saved by grace." You are a lot more than that. You are a new creation in Christ. The New Testament calls you a saint, a holy one, a son of God. In the core of your being you are a good man. Yes, there is a war within us, but it is a civil war. The battle is not between us and God; no, there is a traitor within us who wars against our true heart fighting alongside the Spirit of God in us:
A new power is in operation. The Spirit of life in Christ, like a strong wind, has magnificently cleared the air, freeing you from a fated lifetime of brutal tyranny at the hands of sin and death...Anyone, of course, who has not welcomed this invisible but clearly present God, the Spirit of Christ, won't know what we're talking about. But for you who welcome him, in whom he dwells...if the alive-and-present God who raised Jesus from the dead moves into your life, he'll do the same thing in you that he did in Jesus...When God lives and breathes in you (and he does, as surely as he did in Jesus), you are delivered from that dead life. (Rom. 8:2, 9-11 The Message)
The real you is on the side of God against the false self. Knowing this makes all the difference in the world. The man who wants to live valiantly will lose heart quickly if he believes that his heart is nothing but sin. Why fight?