No matter how carefully you read a great book, one reading is never enough.
Literal
Excellent writing [topic-は] no-matter-how carefully read even-if, once read only [at-では] sufficient is-not.
~にしても ('even if') introduces a concessive clause. どんなに注意深く maximizes the concession — even at peak carefulness, one reading is insufficient. 書物 (しょもつ) is a formal word for 'book' or 'writings,' more literary than 本.