John Eidsmoe, Christianity and the Constitution: The Faith of Our Founding Fathers (Baker 1987).
This is more than a simple discussion of the document itself; it is also a history of the religious ideas that shaped it. Part One, “Background,” discusses how Calvinism, Puritanism, and other religious influences shaped early America and the views of the founders. Part Two, “Meet the Founding Fathers,” examines the particular religious beliefs of thirteen founders and delegates to the Constitutional Convention. In Part Three, Professor Eidsmoe examines the Constitution, the Declaration, and the principles reflected in the words of those documents. It is a fine introduction to many important themes, but at 411 pages, it will take some commitment to finish.