Romans 3:9

What then? are we better than they? No, in no wise: for we before laid to the: charge of both Jews and Greeks that they, are all under sin; and as it is written, There is none righteous, no, not one.

Are we better then they ... is a reference to any supposed Jewish superiority over the Gentiles. Paul had already identified himself, for the purpose of those arguments (Romans 3:7), with the Jews; and that identification is continued here in the words, answer is taken from the Old Testament, from which Paul quotes the sense, but not always the exact words, of a number of passages, the first being Psalms 14:1f and Psalms 53:1f. This blanket inclusion of all people "under sin" is a far greater thing than a mere charge that every man has committed some sin. Griffith Thomas' illuminating passage on this is,

Observe carefully that it is not, as in the KJV, "proved," for he is about to do this from scripture. He has charged them with being under sin. The phrase is very striking: "Not merely sinners, but under the empire of sin" (Liddon). It occurs again with equal force in Romans 6:14; 7:14 and Galatians 3:22. This is the first occurrence of the word "sin" out of nearly fifty places in Romans 1-8. The various New Testament words for "sin" are deeply significant. The most familiar and frequent of them means "missing the mark"; another means "overstepping a boundary"; another, "falling instead of standing"; another, "being ignorant instead of knowing"; another, "diminishing what should be rendered in full"; another, "disobeying a voice"; another, "disregarding a command" and another, "willfully careless." These are but a few of the aspects of sinning suggested by the etymology of the terms used.[19]

There is none that doeth good ... is quoted from Psalms 14:1, and Psalms 53:1,3, and was here directed by Paul against the last stronghold of Jewish presumption, that of any alleged superiority over the Gentiles. This single quotation, reiterated in the Old Testament, was more than enough to sustain Paul's proposition; but he went much further and listed specific sins of Israel and confirmed each with an Old Testament reference. This larger list of twelve specifics was presented by Paul in two sections: (1) sins against their relationship with God (Romans 3:10-12) and (2) sins against fellow creatures (Romans 3:12-18), each class of sins being introduced by the quotation from Psalms 53:3, "There is none righteous, etc."