Ludwig Andreas Von Feuerbach, a humanist-atheist claims that God does not exist.  He explains that God is merely a projection of human imagination. 

He says that man, in his action, is experiencing limitations in this life.  He is going through suffering and poignant pangs of grief in life.  To make up for this limitation, he produced or made up the idea/concept of God who is greater than himself.  

Man, in his limitation, made the idea of infinite, eternal and omnipotent God.  Thus, Feuerbach claims that God is a simple product of human imagination. 

To put into syllogism, he says that “If God is, so man is a slave.  But man is free and intelligent, therefore God does not exist.” 

Granted that Feuerbach was trying to prove the non-existence of God by saying that God is just a product of human imagination in order to satisfy his limitation.  Though he was able to deny the existence of God, still, he was not able to explain where this man’s idea of God comes from.  

The question now is that, if man was able  to make his own idea of God who is greater than himself, where this idea/concept of God comes from? 

Obviously, his idea/concept of God does not come from himself, for man cannot think or even create someone or something which is greater than himself. 

This unsolved question in Feuerbach’s position is answered and explained by Rene Descartes.