Actually, Jefferson was right, but he's being quoted out of context. Christianity is not part of the law. For example, we don't have a national church. On the other hand, the founders were clearly guided by Christian principles.
"History, I believe, furnishes no example of a priest-ridden people maintaining a free civil government. This marks the lowest grade of ignorance of which their civil as well as religious leaders will always avail themselves for their own purposes."
-Thomas Jefferson to Alexander von Humboldt, Dec. 6, 1813.