The inclination to believe in God would be as natural, as rational, as the belief that my memory of having spent last night reading Dickens is reliable. Both beliefs are what epistemologists call properly basic beliefs. They require no evidential support, one is justified in believing them unless and until dispositive evidence is adduced to show that the belief is wrong.
If the inclination to believe is somehow hard-wired into us then there's no need to provide a justification for one's belief that God exists, and the claim by skeptics that belief in God is irrational, a very weak claim in any case, is simply mistaken.
Here's how Barrett frames the question:
Let us take “God” to mean an intentional being or agent with mental states and a will, who can and does act in the natural world. Let us also understand “God” to designate such an agent who has played some role in designing or ordering the natural world, has superhuman access to information about what is the case in the world, and is immortal. With these definitions in mind, then, the big question is: Are typical humans born with such propensities that, under ordinary developmental conditions, belief will likely arise in the existence of at least one God (i.e., an intentional agent who has played some role in ordering the natural world, has superhuman access to information about the world, and is immortal)? If that is our question, then we have reason to think the answer is yes.The question whether there's a natural disposition to believe raises further questions. Is this disposition genetic? If not, what is it? If there is an innate disposition to believe, how do we come to have it? How is the possession of such a trait explicable in evolutionary terms? Does everyone possess it? If so, why does a significant fraction of the world's population not believe?
Lots to chew on. Check out the link.