What does it mean that grace reigns through righteousness?

In Romans 5:21, Paul contrasts sin's reign leading to death with grace's reign that leads to eternal life through Jesus Christ. This means God's grace does not violate His righteousness; rather, it is secured through the perfect obedience of Christ. Grace is not a pardon that overlooks sin; it is the means by which God’s justice is satisfied because Jesus fulfilled the law on behalf of His people. Thus, grace reigns by allowing believers to experience eternal life, not on their merit but through the righteousness found in Christ. This understanding transforms a believer's relationship with sin and reinforces the assurance of salvation.