After destroying any false spiritual security that the Jews would claim from their heritage, their law, or their circumcision (2:17-29), Paul answers the obvious objections by affirming the goodness of God.
After demonstrating that everyone (Gentile or Jew, wicked or moral) will be brought before God's righteous judgment, Paul now turns his focus exclusively on the Jews and destroys any false sense of spiritual security they might have.
People don't care how much you know until they know how much you care; therefore, it is as if Paul writes, "Before I show you my theology, I want to show you myself."