3:28. For we account a man to be justified by faith, without the works of the law.
By faith, etc… The faith, to which the apostle here attributes man's justification, is not a presumptuous assurance of our being justified; but a firm and lively belief of all that God has revealed or promised. Heb. 11. A faith working through charity in Jesus Christ. Gal. 5.6. In short, a faith which takes in hope, love, repentance, and the use of the sacraments. And the works which he here excludes, are only the works of the law: that is, such as are done by the law of nature, or that of Moses, antecedent to the faith of Christ: but by no means, such as follow faith, and proceed from it.
3:29. Is he the God of the Jews only? Is he not also of the Gentiles? yes, of the Gentiles also.
3:30. For it is one God that justifieth circumcision by faith and uncircumcision through faith.
3:31. Do we then, destroy the law through faith? God forbid! But we establish the law.
Romans Chapter 4
Abraham was not justified by works done, as of himself, but by grace and by faith. And that before he was circumcised. Gentiles, by faith, are his children.
4:1. What shall we say then that Abraham hath found, who is our father according to the flesh?
4:2. For if Abraham were justified by works, he hath whereof to glory, but not before God.
By works… Done by his own strength, without the grace of God, and faith in him. Not before God… Whatever glory or applause such works might procure from men, they would be of no value in the sight of God.