How do we know that believers are still sinners?

While believers are redeemed and possess a new nature, Scripture clearly indicates that they still grapple with their old sinful nature. In Romans 7, Paul articulates this struggle, expressing, 'I know that in me (that is, in my flesh) dwelleth no good thing' (Romans 7:18). This reality underlines the importance of grace in the Christian life, as believers acknowledge their ongoing sinfulness and rely on Christ's righteousness. Consequently, Romans 3:23 states, 'For all have sinned, and come short of the glory of God,' indicating that the need for grace is a lifelong reality for every believer.