Revelations speaks about the seven spirits of God. Perhaps, the people who didn't know God as we do, mistook the seven spirits of God as seperate entities. Could this misinterpretation of God's spirits have been the birth of polytheistic religions? 

     However, once God revealed himself to us, we realized that there were not many Gods but one. We now know the seven spirits are all from God. The popularity of the belief system of many Gods has almost died out in modern times because we now understand the source of the spirits.