Professing themselves to be wise, they became fools. The more advanced some of those civilizations got, the more foolish they became because they thought they were so wise. He's probably talking here about the Greeks in particular, who, uh, just put themselves above all mankind. They divided all mankind into two groups. There's the Greeks, and there's the barbarians. Everyone, if you're not a Greek, you're a barbarian. And, you know, we're higher than everyone else.
And yet they came up with these absurd, stupid myths, gods that behave worse than humans, etc.