From the time the world was created, people have seen the earth and sky and all that God made. They can clearly see his invisible qualities -- his eternal power and divine nature. So they have no excuse whatsoever for not knowing God.
Yes, they knew God, but they wouldn't worship him as God or even give him thanks. And they began to think up foolish ideas of what God was like. The result was that their minds became dark and confused.
Claiming to be wise, they became utter fools instead.
And instead of worshiping the glorious, ever-living God, they worshiped idols made to look like mere people, or birds and animals and snakes.
So God let them go ahead and do whatever shameful things their hearts desired. As a result, they did vile and degrading things with each other's bodies.
Instead of believing what they knew was the truth about God, they deliberately chose to believe lies. So they worshiped the things God made but not the Creator himself, who is to be praised forever. Amen.