It is, rather, to make starkly clear the certainty of God's judgment on unrighteousness, which is the terrible consequence of sin. In chapter 1, the Gentiles were not actually referred to, although they were probably in the picture in the minds of some readers, particularly the Jews. In fact, some people, including especially the Jews, would not have regarded themselves as in the category of immoral persons. Yet these very people, in their self-righteousness, were in equal need of conviction of sin. His self-righteousness and moral trends are so strong that he does not feel the need of the Gospel of Christ.
Spiritual pride is a great stumblingblock.
If the man assents to the condemnation of sinners, he really condemns himself. Judging others will not bring escape from God's judgment. The Jew will not be able to claim any exemption because of his national heritage or religion. No human righteousness provides for escape from judgment. Of course, none of these will help a person escape from divine justice.