The declaration of independence is not a legal document, but the letter I posted actually was. It was a treaty with the King (Pasha?) of Libya. If they meant Christinaity, why didn't they specify which god? They may have held some religious views and they may have expressed them at different times, but their legislation we're totally secular.
Any federal law that comes from the Bible is inconsequential... DOMA was as a result of Republican lawmakers responding to the religiosity of their constituents (or perceived religiosity).
When talking about what the nation itself is based on and founded upon, it's clearly secular principles. Jefferson literally said America is in NO SENSE founded on Christianity, it's pretty hard to argue with that