In just 30 short words, Romans 1.21 has so much to say, and none of it is lovely.
People knew God through His out-of-this-world creation! But they chose to not honor Him. They figured it unnecessary to thank Him.
Consequently, their hearts were dark and foolish.
And as to their thinking, they just came up with some very weird ideas.
Paul says that their thinking became futile.
For although they knew God, they did not honor him as God or give thanks to him, but they became futile in their thinking, and their foolish hearts were darkened.
That’s really unfortunate, because thinking can be a rather good asset.