How do we know that faith justifies a sinner before God?

The doctrine of justification by faith is central to Reformed theology and is clearly articulated in Scriptures such as Romans 5:1, which states, 'Therefore, having been justified by faith, we have peace with God through our Lord Jesus Christ.' This verse establishes that faith is the means by which sinners are justified, and it underscores the believer's new standing before God, free from condemnation. This justification is not based on works or merit, but solely on faith in Christ's finished work on the cross, as articulated in Ephesians 2:8-9.

Moreover, justification involves a transformative aspect where true faith results in a changed life. A faith that justifies will also manifest in the believer's actions, as seen in James 2:17, where it states that faith by itself, if it does not have works, is dead. Therefore, while faith is the sole instrument of justification, its efficacy is evidenced by a life that increasingly reflects Christ's character.