I was browsing in How to Read a Book and came across this in the chapter, Reading and the Growth of the Mind:
If the book belongs to the second class of books to which we referred before, you find, on returning to it, that there was less there than you remembered. The reason, of course, is that you yourself have grown in the meantime. Your mind is fuller, your understanding greater. The book has not changed, but you have. Such a return is inevitably disappointing.
Ah yes, I’ve had this experience with the Benjamin Hoff books, The Tao of Pooh and The Te of Piglet. They were informative and entertaining introductions to Daoism (a.k.a. Taoism) back in the day, but after 10 years of taijiquan (a.k.a. t’ai chi) they read as pretty reactionary and actually un-Daoist in the way they explain Daoism.
Adler and Van Doren continue:
But if the book belongs to the highest class—the very small number of inexhaustible books—you discover on returning that the book seems to have grown with you. You see new things in it—whole sets of new things—that you did not see before. Your previous understanding of the book is not invalidated (assuming that you read it well the first time); it is just as true as it ever was, and in the same ways that it was true before. But now it is true in still other ways, too.
How can a book grow as you grow? It is impossible, of course; a book, once it is written and published, does not change. But what you only now begin to realize is that the book was so far above you to begin with that it has remained above you, and probably always will remain so. Since it is a really good book—a great book, as we might say—it is accessible at different levels. Your impression of increased understanding on your previous reading was not false. The book truly lifted you then. But now, even though you have become wiser and more knowledgeable, it can lift you again. And it will go on doing this until you die.
We do not want to state authoritatively that any particular book or group of books must be great for you… Our point, instead, is that you should seek out the few books that can have this value for you. They are the books that will teach you the most, both about reading and about life. They are the books to which you will want to return over and over. They are the books that will help you to grow.
The authors peg the number of great books at “considerably less than a hundred” overall, with fewer than that being great for an individual reader on account of personal taste (not everyone will be turned on by Newton, for instance). It is a bit of a relief to think that there are only a few dozen books that really require, and reward, deep study. Two that come to mind immediately—the Bible and the Dao De Jing (a.k.a. Tao Te Ching)—also happen to be the first and second most popular books ever. I wonder what other classics will end up on my list of inexhaustible books?