Romans one, as others have said. It interesting that these seem to be apostates who willfully walked away.
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.”
It seems that there was a period in their life when their heart had been enlightened. They became vain.
Brother he's talking about mankind
Man began being the glory and image of god
So God created man in his own image, in the image of God created he him; male and female created he them. And God blessed them, and God said unto them, Be fruitful, and multiply, and replenish the earth, and subdue it: and have dominion over the fish of the sea, and over the fowl of the air, and over every living thing that moveth upon the earth. And God saw every thing that he had made, and, behold, it was very good. And the evening and the morning were the sixth day.
Genesis 1:27-28, 31 KJV
They rejected Gods word and exchanged the truth for a lie
And the LORD God commanded the man, saying, Of every tree of the garden thou mayest freely eat: but of the tree of the knowledge of good and evil, thou shalt not eat of it: for in the day that thou eatest thereof thou shalt surely die.
Genesis 2:16-17 KJV
The truth man is made in God's holy image to rule the earth in his ways as srweards and companions of the most high his children
But they rejected the truth and knowledge of God for the lie of Satan
And the serpent said unto the woman, Ye shall not surely die: for God doth know that in the day ye eat thereof, then your eyes shall be opened, and ye shall be as gods, knowing good and evil. And when the woman saw that the tree was good for food, and that it was pleasant to the eyes, and a tree to be desired to make one wise, she took of the fruit thereof, and did eat, and gave also unto her husband with her; and he did eat.
Genesis 3:4-6 KJ
Man was made to be like those who are the offspring of God
Man began here
which was the son of Enos, which was the son of Seth, which was the son of Adam, which was the son of God.
Luke 3:38 KJV
And then they followed Satan and we're corrupted and perverted gods glory they were created to be into this image of Satan
And GOD saw that
the wickedness of man was great in the earth, and that every imagination of the thoughts of his heart was only evil continually. And it repented the LORD that he had made man on the earth, and it grieved him at his heart.
Genesis 6:5-6 KJ
We were made to walk in faith after God as a father and his children but we mankind found that unworthy and chose to become our own God as Satan suggested in Eden we are free we freely chose to reject Gods word and accept Satan's thats what brings Gods what against sin and unrighteousness of mankind
Paul is explaining the conundrum were in and why it came upon mankind God didn't create ys to destroy us because we followed a lie and became evil , that happened because we rejected the truth and accepted a lie
The gospel is an opportunity to accept the truth from the other side and be redeemed from the !ie seared into man's nature to at corrupted us and the answer is always the same if we accept the gospel it's going to change our mind to God which is what man's mind is designed to do hear the lord and what he's telling us and reject the kids that come after we hear it trying to steal it before it roots