Books are not made to be believed, but to be subjected to inquiry. When we consider a book, we mustn't ask ourselves what it says but what it means...

This quote means that we should not assume that a book contains accurate information without evaluating it critically and carefully. We should focus on what ideas the book is attempting to convey, not just take it at face value. Instead of asking what the book says, we should ask what it means. This requires us to inspect the book carefully and evaluate the accuracy of its information and ideas.