How do we know the rule of life for believers is faith in Christ?

This is grounded in the teachings of Paul, particularly in Romans 10:4, which states that Christ is the end of the law for righteousness to everyone who believes. The peace and mercy promised in Galatians 6:16 come to those who walk according to this rule of faith, contrasting with the idea that the Ten Commandments or the law itself provides the moral standard for the believer. Faith in Christ as the sole means of righteousness and salvation is emphasized throughout the New Testament, underscoring that reliance on His obedience fulfills the requirements of the law entirely.