What does the Bible say about the believer's inner warfare?

In Romans 7, the Apostle Paul outlines the internal conflict that believers experience in their struggle against sin. He acknowledges that although he is justified and considered righteous in God's eyes, he still battles with his sinful nature. Paul states, 'for we know that the law is spiritual, but I am carnal, sold under sin' (Romans 7:14). This illustrates the duality of a believer's experience, where they are simultaneously justified before God and yet continue to face the reality of sin in their lives.