Romans 1:21

because that, knowing God, they glorified him not as God, neither gave thanks; but became vain in their reasonings, and their senseless heart was darkened.

'Because that' -'For even though' (NASV)

'Knowing God' -a point that Paul doesn't let us forget (Romans 1:25).

'Glorified him not as God' -They knew more than they did. They didn't hold God in the high esteem that He deserves. Demonstrated in lowering the concept of God (Romans 1:23) 'They did not honor him as God' (RSV).

'I think it may be proved from facts that any given people, down to the lowest savages, has at any period of its life KNOWN FAR MORE THAN IT HAS DONE.'

'neither gave thanks' -ingratitude and human pride the root of false religion-just take. good look at the Humanist Manifesto.

'Vain in their reasonings' -'all their thinking has ended in futility' (NEB); 'their thoughts turned to worthless things' (Beck); 'they busied themselves with silly speculations' (Nor). Reasonings that fail to arrive at any purposeful goal.

'Senseless. -'foolish'. This is the result of abandoning God's truth and engaging in human speculation, you end up with. head full of silly theories, comprehension and understanding are darkened. The "ignorance" that one needs to worry about, is ignorance of the will of God. When Paul was sent to the Gentiles, they were in self-caused ignorance (Acts 26:18).