It's probably the single most important concept in any of the Abrahamic religions: there is only one God. At least that's what God says, over and over. I doubt I have to quote any scripture to convince people of that. But there are times when God himself seems to indicate that there are more. For instance, in Genesis 3, after Adam and Eve eat the forbidden fruit, God says "Behold, the man is become as one of us, to know good and evil" Gen 3:22.
I checked numerous translations, and they all say "us," plural. What is God talking about? Any ideas?