rulers are not a terror to good conduct: Paul presents a positive picture of governing authorities. He describes them according to the role God has given them. Paul does not discuss situations where rulers punish those who do good and reward those who do evil.
Paul was aware of such situations. He knew them from the Old Testament and Jewish history, from the experience of Jesus and the other apostles, and from events in the Greco-Roman world. Here, Paul limits his discussion to how believers should respond to governing authorities who act according to their calling.