In Romans 3:9, Paul tells us that sin is a real force. It dominates and enslaves. Verse 10 moves on to prove his statement by quoting from the Old Testament, then having stated that both Jews and Gentiles (V9) are under sin, he clinches the argument by the Jewish Scriptures which they could not deny. Man left on his on would not seek God. We would wallow in sin enjoying every minute of it, if not for the conviction of the Holy Spirit, that draws us to God. The Jews thought they had an advantage because they were entrusted with the oracles of God. Jesus was hated by the Jews because He showed them the errors of their belief. Paul is hammering this home in Romans 3, that there is no advantage to being a Jew, because ALL are sinners, Jew and Gentile alike. They did not want to hear this.