Man"s basic rejection of God's deity (21a, 23). Man refused to honour God and refused to give Him thanks. Instead, man humanized God.
Man's rejection of God's revealed truth (19, 20, 21b, 22). What can be unknown about God is plain to men, that is, His eternal power and deity. But men suppressed the truth by their wickedness. As a result, man's wisdom has ended in futility and darkness. "Professing themselves to be wise, they became fools."