God worries about other gods again...

Deuteronomy 18:20, says, "But the prophet, which shall presume to speak a word in my name, which I have not commanded him to speak, or that shall speak in the name of other gods, even that prophet shall die." Ummm after Deuteronomy 18:15, once again we have a mention of other gods. Why is an omniscient omnipotent being who knows he is the only one, so paranoid? Were the writers of this book unsure that their god was the only god? It makes you wonder?