Maybe just me, but it seems that the oldest beliefs were those which were also the closest to understanding the true nature of things. I believe that nature is the true manifestation of whatever "God" is. Those who lived in harmony with nature, were also those who were truly at one with "God". It was more than just a mere religious belief, it was an intimate connection and a harmonization with an unseen reality. A reality that was shared with the plants, the rocks, the animals and all of existence.
I believe there is a reason why it is said that Jesus and Muhammad, and Buddha....heck even Odin for that matter, sought out the solitude of nature or to be near a tree to gain their spiritual "enlightenment". It is not surprising to me at all. It just seems "natural". They knew where to find "God". And it was not in books.