...we know that "An idol is nothing at all in the world" and that "There is no God but one." (1 Corinthians 8:4, NIV)
In all the world, there is but one true God. How do I know? The Bible tells me so.
Hear, O Israel: The LORD our God is one LORD: (Deuteronomy 6:4)
For there is one God and one mediator between God and mankind, the man Christ Jesus, (1 Timothy 2:5)
Only fools say there is no God. (Psalm 14:1)