One answer is that people believe in God because they are socialized into such a belief. This is certainly true for most Americans. But, this response begs the question of why people believe in God, because at some point, somehow such belief had to start. It had to be invented. So, then, the question is why did people in the past invent God? And the answer is, "We don't know"—not in the scientific sense of knowing. There is no documentation, no evidence available to us to answer the question. We can speculate, but in the absence of even the possibility of evidence our speculations one way or the other carry no weight. So, while socialization is an explanation for why individuals believe in God, it does not explain why there is such a belief. We don't know why it exists to be socialized.
Another answer is that people believe in God because they have experiences that they interpret to be divinely inspired. These experiences are various and include such things as visions and deep spontaneous feelings (of peace, of holy terror, of profound love) experienced while in nature, while meditating/praying, while in group exercises (worship), and even while under stress. But, again, the fact that people have experiences of God only explains why individuals believe in God. Such experiences provide no evidence as to where they come from or why they should even exist at all. Possibly, those who invented belief in God associated certain experiences with a notion of a divine being (or beings) or "spirit-ual" reality of some kind, but if that is what happened why did they make such a connection? Why did the inventors of belief in God believe in God? The answer is that we have no way of knowing.
The point here is that for those who put their faith in God faith is exactly that: faith. It involves received traditions (socialization), personal experiences, pious exercises (worship, meditation, prayer) and reflection on "what makes sense," but at the end of the day it is faith—faith that there is a deeper, divine Reality beyond the socialization, experiences, and the reflection. That faith can be compelling or it can be mildly interesting, profound or superficial, thought through carefully or blithely accepted at face value; but in all of this it is a faith that "makes sense" to the faithful. While we don't know, then, why people believe in God, those of us who do have a sense that there is more to reality than what science or the senses perceive, something Deep, Powerful, and profoundly Creative. For Christians, we sense that we come closest to that Something in Jesus of Nazareth, and we trust that our sense of the holy is so. We trust in him that it is so. Amen.
