I think that it is important to understand that God is the same yesterday, today and forever. Hebrews tells us that it is impossible to please God without faith, that one must first believe that he is and that he is the rewarder of those who diligently seek him. Romans said he gave himself witness through creation. And in yet another place God did not leave himself without witness as he sent rain from heaven.
To come to God in prayer one must first believe there is a chance God exists. That is enough to get a response.
Gary