The Constitution never mentions, most of the Forefathers were Deist. In my interpretation of that belief is that there is a God, but he does not reveal himself to humans in this life.
I always remember from my history readings that George Washington just wanted all Americans to stop persecuting the Catholics. The new country wanted to break away from the Church of England, they thought it was wrong to dictate that upon the country. That is why they made sure that in this new country all Americans could worship the way they wanted. That included all faiths.