Why do chrisitians maintain that there is only one god when the bible makes it clear that there are many? [Spirituality & Religion]

If there is only one god, why do we have the worlds "El" and "Elohim"? One singular, one plural, both used by the god of the bible.
Why do we have god telling us to worship no OTHER gods before him? Why are there references to "we" to "I" ? Obviously there would be no competition between a fake god who couldn't do anything and real god who could grant miracles and punish the unfaithful.