How do we know the doctrine of salvation by grace alone is true?

The doctrine of salvation by grace alone is grounded in the biblical affirmation that righteousness and justification come solely through faith in Christ. Romans 3:21-24 states that righteousness is apart from the law and attainable through faith in Jesus Christ, who fulfilled the law and redeems those under it. The Apostle Paul emphasizes in Galatians that believers cannot achieve salvation through their efforts or adherence to the law; instead, they are made free by grace through faith (Ephesians 2:8-9). This principle of grace is what differentiates the gospel of Christ from legalism and underscores the sufficiency of Christ's sacrifice for salvation.