God is making it clear to all non-Jewish people who are godless and wicked that he is angry with them.

Romans 1:18

18 From where God rules in heaven he is making it clear to all non-Jewish people who show no respect for God and who do wicked things, that he is angry with them and that they deserve to be punished {that he would punish them} [MTY]. By means of their behaving wickedly, they keep other people from believing what they know to be true about God.