§ 02 · King James Bible
Romans 1:21
Because that, when they knew God, they glorified him not as God, neither were thankful; but became vain in their imaginations, and their foolish heart was darkened.
Simple English
Since they knew God, they didn't give him the praise he deserved nor showed gratitude. Instead, they thought up silly ideas and their minds got confused.
* Work in progress - there may be occasional inaccuracies