The Divine Author wrote two books: the Bible and the Book of Nature. This last title, "the Book of Nature", is obsolete. Galileo Galilei used it in a very significant way. Usually historians use it in connection with Galileo. Obviously, they find it exciting. No one explains this excitement. The title itself is puzzling: the Book of Nature is not a book proper. Some read the expression as a synonym for "Nature". They are in error. Galileo asserted that the language of the Book of Nature is mathematical. The Book of Nature then is not a set of natural phenomena. It is a set of natural laws. It is, strictly, a book of laws. Alternatively, "The Book of Nature" is a loose metaphor. It stands then for reason and its products. I propose that the right reading includes both the strict and the loose sense of the title. "The Two Books' is a metaphor on the uneasy relations between faith and reason.