Believe whatever you want
But the words God, Creator, are used in the pledge of allegiance, bill of rights, declaration etc
The founding fathers knew about religious freedom. Christianity isn't a religion, its a philosophy.
The christian principles are easily found, use google. All men are created equal, inalienable rights, endowed by our Creator etc etc. Etc
Now you're just arguing to argue. The country was founded on christian principles, that's is just pure fact.