Despite the name, Hazel Grace definitely isn't the religious type. But for many people, religion goes hand-in-hand with dying. Augustus's parents take real comfort in their belief in God; Patrick, who runs Support Group, also encourages the kids to turn to religion as they face down their own deaths. Whether or not the characters in The Fault in Our Stars take comfort in religion, though, its presence clues us in to the many different ways people cope during the toughest times.
All of the characters in The Fault in Our Stars have a different approach to religion, which is inextricably linked to how they are dealing with their mortality or the mortality of those that they love.
Even though Hazel is not religious and finds it at odds with intellectualism, her perspective changes when she has in-depth conversations with Augustus and her father, who both have their own take on spirituality.