Robert P. Crease explains the context and purpose of Galileo's metaphor of the book of nature: Galileo intended it to emphasize 'that the signs of nature had their own self-contained meaning', independent of Biblical exegesis. In his conclusion, though, Crease expresses these reservations:
But the image of the book of nature can haunt us today. One reason is that it implies the existence of an ultimate coherent truth - a complete text or "final theory". While many scientists may believe this, it is ultimately only a belief, and it is far likelier that we will endlessly find more in nature as our concepts and technology continue to evolve. Furthermore, the image suggests that the "text" of the book of nature has a divine origin...While one can't deny that the book metaphor does indeed suggest the idea of an author - or at least authors - it is also the case that metaphors by their nature are only ever meant to indicate partial likenesses. That the news came as a hammer blow to Mildred doesn't mean it was delivered by a blacksmith. And any sophisticated understanding of how readers relate to a text must surely allow plenty of room for the possibility of finding new concepts and understandings which earlier readings had overlooked. One doesn't have to think the interpretation of texts is subject to no constraints at all to recognize that they don't contain a single definitive truth. (Via A&L Daily.)