Paul wrote to the Galatians in 2:15-16: We who are Jews by nature, and not sinners of the Gentiles, Knowing that a man is not justified by the works of the law, but by the faith of Jesus Christ, even we have believed in Jesus Christ, that we might be justified by the faith of Christ, and not by the works of the law: for by the works of the law shall no flesh be justified. The phrase we are Jews by nature simply refers to those who were born Jews including Paul. As for the rest of us, we were the sinners from among the Gentiles.
However, please understand that Paul was not saying that the Jews were not sinners as well. He had said as much in Romans 3:23 when he said that all have sinned and come short of the glory of God. It also needs to be understood that Paul here was not addressing all Jews but only those who know that a man is not justified by the works of the law, but by the faith of Jesus Christ. The language makes it clear that he is addressing those Jews who had placed their faith in Christ and not the Law. This would mean that they were grace believers.
Again, he said that by the works of the law shall no flesh by justified. This has to be referring to the new dispensation of grace because under the old dispensation of Law they were justified by the works of the Law. Paul said in Romans 2:13, For not the hearers of the law are just before God, but the doers of the law shall be justified. This verse is clearly not referring to this present dispensation of grace.
Also, James 2:20-26 also said the exact opposite when he said, But wilt thou know, O vain man, that faith without works is dead? Was not Abraham our father justified by works, when he had offered Isaac his son upon the altar? Seest thou how faith wrought with his works, and by works was faith made perfect? And the scripture was fulfilled which saith, Abraham believed God, and it was imputed unto him for righteousness: and he was called the Friend of God. Ye see then how that by works a man is justified, and not by faith only. Likewise also was not Rahab the harlot justified by works, when she had received the messengers, and had sent them out another way? For as the body without the spirit is dead, so faith without works is dead also.
It is pretty apparent that Paul and James are contradicting each other in these verses. What gives? The men were obviously saying two different things because they were addressing different audiences. Paul was the apostle to the Gentiles and James was writing to the Jews who were still under the Law. Like many in the church today, I spent years trying to harmonize the glaring contradictions until I came to realize that.