Connections - Chapter Three: Religion

In Billy Pilgrim's office at work, there is a prayer on the wall that goes "God, grant me the serenity to accept the things I cannot change, courage to change the things I can, and wisdom always to tell the difference." The the previous chapter Billy talks about a crucifix that his mother gave to him. Billy Pilgrim is not a religious man, so why does Vonnegut throw in these religious references? Kurt Vonnegut described himself as an atheist, so why would he want to include objects that talk about religion? I think he is trying to show that in times of despair, many turn toward religion for comfort and solace.