If you dont mind I will answer the question on an evolutionary basis.
As our ancestors brain functions increased, due to the ever wider set of environmental conditions we faced as a result of our rapid expansion out of Africa, we somewhere along the way developed the sense of time. Probably in part due to synchronising our nomadic encampments with animal migrations. With that sense of time and our other capacities of speech and artistic expression we began to ponder our place, the big questions of where from, where to and why. We only had nature back then of course and we of course drew from that. Gods were represented by animals and constellations because that was our world. As we settled into non-nomadic townships we began to lose touch with nature and our Gods became anthropomorphisised. Just as our art developed in complexity so did our religions, or belief systems. Whatever our state of cultural evolution it was reflected in the belief systems.
It is probably always been a fact that mankind has sought to authenticate each system by invoking historical longevity, the myths once passed down in the oral tradition were adapted and written down. The bible has most of its content found in more ancient polytheistic traditions of the same geographical area. So in fact our Gods are hand me downs from the myths captain caveman used to tell around the campfire to keep his tribe entertained at the dawn of our species. And it is quite amazing that we are no less superstitious now than we were back then.
It should also be noted that belief systems also became an important part of social identity. This is what gave rise to diversity amongst religions. And of course was all to often, and continues, to be used by power-lusters to polarise and engage in conflict other groups. Nothing in modern society ties us closer to the dawn of our race than religion. Its high time we dumped the superstitions and evolved into a new race. Homo Superstitious did us proud, but its time to move on.