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.
One of the root causes of a culture's decline as described in Romans 1:24, 26-32 is the cold thanklessness of those in the culture who know God. The source of this thanklessness is, according to this verse, the result of a change in their way of thinking, or, perhaps more correctly, in the focus of their thoughts. The phrase in this verse “but became vain in their imaginations” means: “their thoughts became directed to worthless things.” Bauer-Danker
So the visible downgrade of a people who know God begins when they fail to discipline their minds to be appropriately vocal and sincere in their thankfulness to God. Growing out of this thanklessness, according to Romans 1:23,25, comes a movement to redefine God. To devise a new god more suitable to their new way of thinking... a more practical god. This all happens over time.
There is more in this section of Scripture than I can begin to touch in a short post, but let me just point out a few major truths which are laid out on the surface for us all to see: God listens for our thanks giving, observes the focus of our thoughts, and He measures our beliefs about His being. Based on His experience with us in these matters He decides to extend or withdraw His mercy. And His mercy is the foundation of the moral prosperity of any people. His mercy and our thankfulness are intertwined. It could be said that mercy rides on the wings of thanks giving.
God walks among us... especially those of us who know Him. Let us focus our minds upon Him, and let us appropriately thank Him without redefining Him. Our nation depends on our accuracy and faithfulness in this matter.