In verse 12 he has spoken only of those who have sinned: the Gentiles without the law, and the Jews having the law. Both classes of men are guilty.
So strong is self-delusion that people imagine all manner of extraordinary grounds on which to believe God favours them – church attendance, Christian parents and a Christian upbringing, a morally upright life, or respectability in society. All these things leave the issue of sin unaddressed, and the sinner still in a state of condemnation. This must be made clear before anyone is ready to hear the gospel.