1. What are the statements about what you call "God" that you believe in?
2. Why do you believe just that set of statements and not some other set of statements?
I believe that the answer to 2., if they are honest, would most often be: They believe the set of statements they believe because they WANT to believe just those statements. And why do they want to believe just such a set of statements? Because believing what they believe makes them feel good.
They want to believe those statements, and here's the minor miracle: Just because they want to believe those statements, they also all of a sudden do believe them. At least they claim they do.