"Boasting is the language of our fallen self-centredness. But in those who have been justified by faith, boasting is altogether excluded ... our Christian conviction is that a sinner is justified by faith, indeed by faith alone apart from observing the law. Whether those "works of the law" which Paul had in mind are ceremonial (observing rules for diet and the Sabbath) or moral (obeying God's commandments) they cannot gain the favour or forgiveness of God. For salvation is "not by works so that no-one can boast". It is only by faith in Christ which is why we should boast in Him and not in ourselves".
John R W Stott - "BST Series - The Message of Romans" - IVP, Leicester (1994) - (p119).