Books (or other relevant sources of information) provide an essential starting point for learning how to compose music. They help aspiring composers to build a strong foundation which can then be developed/expanded. Initially, an aspiring composer's music may sound "by the book" but they could be innovative after they are confident that they have mastered the principles of composition and become competent at composing music.
"You do this by learning the language of classical music". How could someone learn the language of Classical music?Firstly, by acquiring knowledge about how to compose music in a Classical style from a book/books or any other relevant sources of information. Secondly, by emulating the style of Classical music by using the methods that have been described in the quote above or by using any other method.
Find the best book you can find on ear training. When you're done with that, then transcribe, transcribe, transcribe.Then you'll be in an excellent position to start composing.