What does Romans 3:12 mean?

Paul is quoting from Psalm 14 to show that his bold statements are not new ideas, even if the Jewish religious leaders have misunderstood or forgotten them. Judging by Paul's remarks here, it was commonly held that the Jewish people had the law and were circumcised, therefore they were therefore a righteous people in God's eyes. This would have led people to feel protected from God's judgment. Paul has contradicted that idea, teaching that every individual person will be judged by God for their actions, whether right or wrong. And every one of us will be found to be "under sin" and deserving of God's anger. Verse 10, which began this citation, makes this clear by stating that there is "not one" who is naturally righteous.

Paul's paraphrase of David's words in Psalm 14:3 describes what God found when he searched humanity looking for any righteous—sinless—people. Of course, God already knew the outcome, but Scripture states this to emphasize that it's something clear and obvious. We have all turned aside from following God's path. We have all become worthless; we are all corrupt. Not one single person is found to do good, by the standards of a holy and perfect Creator.

Neither of these Scriptures implies that no human ever does anything that can be described as good. Of course, people do isolated good things all of the time, at least by our standards. We are capable of knowing the difference between right and wrong, and choosing what is right…when we want to. The ultimate problem, as David wrote and Paul agreed, is that nobody's heart is naturally oriented toward doing good. We are all, every one of us, pointed in a self-serving direction and away from God's definition of goodness.

The bottom line is that humans are capable of doing good, but we universally choose not to, by God's standards. We want what we want and not what He wants.