In the second chapter of the letter to the church at Rome, Paul continues his reasoning with his gloves off. He’s not pulling any punches; he is laying his understanding of the life in Christ out for the “saints” in Rome to understand.
In the first chapter, Paul rather took the Gentiles on. Realize, if I may over-simplify, that at this point in the first century, people could be broadly characterized as either Jews or Gentiles. Jews were the people of God, the descendants of Abraham. Anyone who was not a descendant of Abraham was seen as a Gentile—someone (according to the Jews) outside the circle of God’s love and acceptance.
Having pretty well established that Gentiles were a sinful lot (and in so doing, making the Jews feel better about themselves) Paul lowered the boom on the Jews, firmly establishing them to be deserving of God’s wrath like everyone else.
Boy, that’ll make you feel all warm and fuzzy.
We are accustomed to reading narrative stories that have a simple beginning and end—but with Romans (as with all the epistles) we are reading parts of logical arguments. Slow down your reading; expand your thinking and listen to what God is saying through Paul.