Romans 1:22

To be wise. Paul is not here referring simply to the pretensions of Greek philosophy, although he placed a low estimate on such wisdom (1 Cor. 1:18-25). He is describing the conceit of those whose wisdom is connected with any willful departure from divine truth and out of which idolatry must have originally sprung in its many and fantastic forms. Men turned away in their supposed wisdom from the true knowledge of God, and heathenism was the inevitable result.

Became fools. The climax of their folly was idolatry (see Jer. 10:14, 15, for what foolishness could be greater than to worship an animal instead of God?