In Chapter 1, Paul greets the church in Rome and explains how he cares about them. Then, he goes on to explain the gospel. He starts by speaking about God's righteous wrath against all ungodliness and unrighteousness of men. Men suppresses the truth in their unrighteousness and exchange the truth about God for a lie and worship and served the creature rather than the Creator.
In Chapter 2, Paul anticipates that his audience will agree with him about God's righteous judgement, but not think that God's judgement applies to them. These are Christian Jews and Christians gentiles. They know God will judge evildoers, but they don't think God will judge them. They think they are invincible. So Paul shifts from speaking generally about mankind, to speaking specifically about his audience.