Romans 11:30-31 : For as ye in time past were disobedient to God, but now have obtained mercy by their disobedience, even so have these also now been dis-obedient, that by the mercy shown to you they also may now obtain mercy. Here it seems that Paul speaks especially to Gentile Christians. Though the Gentiles had not been under the law of Moses, yet they had been disobedient to God. If, as some say, Gentiles were not under any law of God, how could Paul say they had been disobedient to God? The truth is, all people are, and have always been, under God's eternal moral law, a law inherent in the nature of our relations to one another. The Gentiles, in disobeying this moral law, had sinned against God.
For a list of their sinful practices see Romans 1:18-32. They were therefore under condemnation, as much so as were disobedient Jews. But mercy had been extended to these Gentile sinners; the opportunity to turn from their sins and be saved had been granted to them in the gospel. And this was a guaranty that disobedient Jews also could obtain mercy.