27 Then what becomes of our boasting? It is excluded. By what kind of law? By a law of works? No, but by the law of faith. 28 For we hold that one is justified by faith apart from works of the law. 29 Or is God the God of Jews only? Is he not the God of Gentiles also? Yes, of Gentiles also, 30 since God is one—who will justify the circumcised by faith and the uncircumcised through faith. 31 Do we then overthrow the law by this faith? By no means! On the contrary, we uphold the law.
John Murray, in his commentary on Romans (Murray, John. The Epistle to the Romans: the English Text with Introduction, Exposition and Notes. Grand Rapids: Eerdmans, 1968.) discusses the relationship between faith and works of the law:
We are required to ask how the principle of faith is so rigidly exclusive of and antithetical to works of law in the matter of justification. The only answer is the specific quality of faith as opposed to that of works. Justification of works always finds its ground in that which the person is and does; it is always oriented to that consideration of virtue attaching to the person justified. The specific quality of faith is trust and commitment to another; it is essentially extraspective and in that respect is the diametric opposite of works. Faith is self-renouncing; works are self-congratulatory. Faith looks to what God does; works have respect to what we are. It is this antithesis of principle that enables the apostle to base the complete exclusion of works upon the principle of faith ... It follows therefore that "by faith alone" is implicit in the apostle's argument. Luther added nothing to the sense of the passage when he said "by faith alone". (123)