We often think our conflict with sin stems from two natures struggling within: the sin nature of our flesh set against our redeemed inner man. “My higher nature should be victorious over my lower nature,” we’re taught. So when we sin, it’s hard to understand how we could be so weak. “Shouldn’t I be something more than what I so obviously am? What’s wrong here?”
Well, let me rock the boat a little: We’re not seeing a battle between two natures here, but merely witnessing human nature in action. What we’re really sensing is two kingdoms, each tugging at us. Our basic nature doesn’t change once we’re saved. I’m still the same old human me. What’s happened is our spirit, no longer dead because of sin, is now capable of functioning for the purpose it was created for. We’re alive to God! Our spirit has become united with the Spirit of God within.
From Free from the Power of Sin: the Keys to Growing in God in Spite of Yourself