What does the Bible say about being simultaneously righteous and a sinner?

The concept of 'simul justus et peccator,' meaning simultaneously righteous and a sinner, is rooted in the Christian understanding of justification and sanctification. According to 2 Corinthians 5:21, believers are made righteous not through their own works but by faith in Christ, who bore our sins. Romans 7:18-19 illustrates the internal struggle every believer faces: while we desire to do good, our sinful flesh remains unchanged. This tension reflects our identity in Christ as righteous, contrasted with our ongoing battle against sin.