1 What advantage then does the Jew have? Or what profit is there of circumcision? 2 Much in every way. Chiefly, because to them the oracles of God were committed. 3 For what if some did not believe? Will their unbelief make the faith of God without effect? 4 By no means. Truly let God be true, but every man a liar, as it is written, "That you may be justified in your sayings and may overcome when you are judged."
5 But if our unrighteousness commends the righteousness of God, what shall we say? Is God unrighteous who takes vengeance? (I speak as a man.) 6 By no means. For then how shall God judge the world? 7 For if the truth of God has more abounded through my lie to his glory, why yet am I also judged as a sinner? 8 Why not rather say (as we are slanderously reported, and as some affirm that we say), "Let us do evil so that good may come"? Their condemnation is just.
9 What then? Are we better than they are? No, in no way. For we have before proved both Jews and Gentiles, that they are all under sin,
10 As it is written, "There is no one righteous, not even one.
11 There is no one who understands. There is no one who seeks God.
12 They have all gone out of the way. They have together become unprofitable. There is no one who does good, not even one."
13 "Their throat is an open sepulcher. With their tongues they have used deceit." "The poison of asps is under their lips,"
14 "Whose mouth is full of cursing and bitterness."
15 "Their feet are swift to shed blood.
16 Destruction and misery are in their ways.
17 And the way of peace they have not known."
18 "There is no fear of God before their eyes."
19 Now we know that whatever things the law says, it says to those who are under the law so that every mouth may be stopped and all the world may become guilty before God. 20 Therefore, by the deeds of the law, no flesh shall be justified in his sight, for by the law comes the knowledge of sin.
21 But now the righteousness of God without the law is manifested, being testified by the law and the prophets, 22 Even the righteousness of God, which is by faith of Jesus Christ to all and upon all those who believe, for there is no difference. 23 For all have sinned and come short of the glory of God, 24 Being justified freely by his grace through the redemption that is in Jesus Christ, 25 Whom God has set forth to be a propitiation, through faith in his blood, to declare his righteousness for the remission of sins that are past, through the forbearance of God, 26 To declare at this time his righteousness, so that he may be just and the justifier of him who believes in Jesus.
27 Where is boasting then? It is excluded. By what kind of law? Of works? No, but by the law of faith. 28 Therefore, we conclude that a man is justified by faith without the deeds of the law. 29 Is he the God of the Jews only? Is he not also of the Gentiles? Yes, of the Gentiles also, 30 Seeing that it is one God who will justify the circumcision by faith and the uncircumcision through faith.
31 Do we then make the law void through faith? By no means. But we establish the law.
[v.4] - Quoting Psalm 51:4 (LXX).
[v.10-18] - It is likely that Paul is quoting Psalm 14:1-3 from the Septuagint in all of these verses (though, in the Septuagint, it's Psalm 13). Verses 10 and 11 go with Psalm 14:1-2, with verse 11 being a paraphrasal of Psalm 14:2, and verses 12 through 18 are from Psalm 14:3. In the Septuagint, Psalm 14:3 contains all of the text Paul quotes in verses 12 through 18. It is unknown whether Paul had the verses from the Septuagint or if he strung together the verses from the various other places they are found in the Old Testament. Since Paul frequently quotes the Septuagint, I'm inclined to think that is what he is using for the source of these verses he is quoting. See the note for Psalm 14:3 to see the full text of the verse from the Septuagint.
[v.10a] - Quoting Psalm 53:1. See also, Psalm 14:1.
[v.10b] - Reference, Ecclesiastes 7:20; Galatians 3:22.
[v.11] - Quoting Psalm 53:2 (paraphrased).
[v.12a] - Quoting Psalm 53:3.
[v.12b] - Reference, Ecclesiastes 7:20.
[v.13] - Quoting Psalm 5:9 (LXX), 140:3 (LXX).
[v.14] - Quoting Psalm 10:7 (LXX).
[v.15-16] - Quoting Isaiah 59:7 (LXX).
[v.17] - Quoting Isaiah 59:8 (LXX—paraphrased).
[v.18] - Quoting Psalm 36:1 (LXX).
[v.19] - Reference, Psalm 14:1, 53:1; Ecclesiastes 7:20; Romans 3:10, 23; Galatians 3:22.
[v.23] - Reference, Psalm 14:1, 53:1; Ecclesiastes 7:20; Romans 3:10, 19; Galatians 3:22.