Paul has shown in chapter 1 that the Gentiles, as a whole, were degenerate sinners and deserving of God's wrath. But his object is not merely to condemn that segment of humanity. He used it as a diplomatic approach to prove to the other segment, the Jews, that they also were sinners and just as worthy of judgement. This is an important step to achieve his primary object and that was to lead the Jews to see their need of salvation; to see that salvation comes, not through their descent from Abraham, or by a careful, meticulous adherence to law, but only through Jesus Christ.
"Therefore thou art inexcusable, O man, whosoever thou art that judgest: for wherein thou judgest another, thou condemnest thyself; for thou that judgest doest the same things." Obviously Paul is not here thinking of judging in the sense of weighting an individual in an attempt to discover his sincerity, honesty, or worth. This we must do often. He has in mind judging with a view to condemning a person.
Like a lawyer, Paul has been making his case against what may appear to be only accused...the Gentile. And the Jewish judge, sitting high and complacent on his judgement seat (and this does not exclude the Gentile judge), is nodding his complete agreement with the verdict of guilty passed upon the Gentiles. But now, having set his trap, Paul springs it. Turning to the judge, he says, "You agree that the gentiles are wicked, and thus worthy of the wrath of God. In that case you must also agree that you deserve the same judgement, for you who passes judgementon them are guilty of the same evils." The Jews considered themselves as the chosen people of God, even after they had rejected Him and He had rejected them. They thought of themselves as the only people in the world that God loved. And they, like the god they had created in their hearts, despised the wicked Gentiles.
In the Jews' attitude toward the Gentiles we see a common failingof all humanity. It seems to be a part of human nature to attack in the person of others, faults in ourselves which we refuse to admit. "Those who are most ready to excuse or justify themselves in sin are often most severe in judging and condemning others. There are many today, like Saul, bringing upon themselves the displeasure of God. They reject counsel and despise reproof. Even when convinced that the Lord is not with them, they refuse to see in themselves ... the cause of their trouble. How many cherish a proud, boastful spirit, while they indulge in cruel judgment or severe rebuke of others really better in heart and life than they. Well would it be for such self-constituted judges to ponder those words of Christ: “With what judgment ye judge, ye shall be judged; and with what measure ye mete, it shall be measured to you again”. {St 08-17-1882}.