How do people who reject God in their knowledge think about God and eternity?
People who reject God in their knowledge have no concept of the things of God and no concept of eternity. They live only for the here and now. Because they did not want to retain God in their knowledge, God gave them over to a reprobate mind.
Les explains from Romans 1:28 that those who did not like to retain God in their knowledge have no concept of the things of God and no concept of eternity; they are just living for the here and now. Because that is the way they wanted to live, God gave them over to a reprobate mind, and that reprobate mind causes them to do things which are not convenient, not normal, or not natural. They are filled with all unrighteousness, which is the opposite of righteousness, and this fits with Galatians chapter 5. Earlier Paul also said such people will not inherit the Kingdom of God.
And even as they did not like to retain God in their knowledge, God gave them over to a reprobate mind, to do those things which are not convenient;