How do we know that believers will not be condemned?

Believers in Christ are not condemned because their sins have been imputed to Him, and He has paid the full penalty for those sins. Romans 4:5 states that faith in Christ, who justifies the ungodly, grants righteousness apart from works. This means that when a person truly believes in Jesus, they are justified—declared righteous in God's sight—because their sins have been borne by Christ. Therefore, their current standing is one of forgiveness, and they will not face the condemnation that their sin deserves.