The General Description Of Man's Sinfulness (3:10-12).
These verses are very much a rough paraphrase of Psalms 14:1-3 which runs as follows in MT:
“ There is none who does good. The Lord looked down from Heaven on the children of men to see if there were any who did understand, who did seek after God, they are all gone aside, they are together become filthy, there is none who does good, no, not one. ”
In LXX it reads, “ There is none who does goodness, there is not even so much as one. The Lord looked down from heaven on the sons of men, to see if there were any that understood, or sought after God. They are all gone out of the way, they are together become good for nothing, there is none who does good, no not one. ”
It will be noted that there is little difference between his words and theirs but that, where there is, Paul's paraphrase is closer to LXX. The main difference lies in the fact that he omits ‘God looking down from Heaven to see if --', replacing it with ‘there is'. The alteration from ‘good' to ‘righteous' is probably Paul's in order to bring it into line with the subject that he is dealing with, the righteousness of God. The emphasis then is on the fact that there is none righteous in God's eyes. There is none who is ‘in the right'. But this necessarily follows if they are not righteous.
The point of the citation is in order to bring out man's universal sinfulness. All are included as sinners. None as they are in themselves do what is righteous, not even one. None understand. None seek after God. All have turned aside from the true path, all have become profitless, useless, good-for-nothing. None do good, no not one.