My main purpose is writing this letter is to tell you how grateful I am that you published this book because I have learned many, many things from it that can't be learned in a textbook.
寫這封信最主要的目的，就是告訴你們，我真的非常感謝你們出版這本書，因為我自其中學到了非常非常多教科書上學不到的東西。