for all have sinned and fall short of the glory of God,
23. There is indeed no difference, etc. He urges on all, without exception, the necessity of seeking righteousness in Christ; as though he had said, “There is no other way of attaining righteousness; for some cannot be justified in this and others in that way; but all must alike be justified by faith, because all are sinners, and therefore have nothing for which they can...
From all this Paul infers that it is in vain to look for justification by the works of the law, and that it is to be had only by faith, which is the point he has been all along proving, from Rom 1:17, and which he lays down (Rom 3:28) as the summary of his discourse, with a quod erat demonstrandum - which was to be demonstrated.
Commenting on Romans 3:19-31
Where is boasting then?.... There is no room nor reason for it, either in Jews or Gentiles: not in the Jews, who were very apt to boast of their being Abraham's seed; of their circumcision; of their being Israelites; of their having and keeping the law; of God being their God; and of their knowledge of him: nor in the Gentiles, who were ready to...