A reader carefully evaluates the theme of a book:

because it may disagree with the popular views of life

because it may raise unanswerable questions in the reader's mind

because it may not encourage the reader to improve himself

because it may present values and ideals directly opposed to those of the reader

A reader carefully evaluates the theme of a book because it may present values and ideals directly opposed to those of the reader. We read books basically to learn and improve ourselves. Usually we select books according to our subjects of interest and so does the theme. We evaluate the theme that conforms to our values and ideas.