Q:

You will read in a book that (correct?)

I was reading a story called "The Journey to Hanford" in a book titled "Great American Stories 1" by "C. G. Draper".
In that story, I found the expression "You will read in a book that..." about three times. But to me, a non-native English speaker (an English learner), I find confusing the use of that expression and was wondering if its use is correct.
Here is the context:
Example 1:

"I won't have him singing all day," my grandfather roared. "Some
  things simply have to stop, in the end. You will read in a book
  that a father loves a foolish son more than his wise sons. Believe
  me, that writer is not married, and also he has no sons."

Example 2:

"Away with him and his zither both," my grandfather said. "You will
  read in a book that a man can sit all day under a tree and play
  music on a zither and sing. Believe me, that writer is a fool. Money,
  that's the thing. Let him go and The Journey to Hanford work under the
  sun for a while. In the watermelons. Him and his zither both."

Example 3:

"Foolish words!" my grandfather said. "You will read in a book
  that a man who sings is truly a happy man. But that writer is a
  dreamer, not a businessman in a thousand years. Let him go. It is
  twenty-seven miles to Hanford. That is a very good distance."

If it's correct, is it really expressing future? What kind of future? 
I have never heard that expression before. I don't think it's really expressing the future. I can't find it anywhere neither in a book (except the one when I found it) nor on the internet.
I would expect something like "You may/might read in a book that" instead. So I would expect something expressing possibility or the past tense.

A:

I looked up your quotations on the internet and discovered that they were  from a short story written by William Saroyan which is indeed called "The Journey to Hanford." Judging from its description on Amazon, the book you have, "Great American Stories 1", contains stories that have been "adapted" for English learners by the editor C.G. Draper.
C.G. Draper made an excellent choice when he included this story in his collection because Saroyan writes in a very straightforward, uncomplicated style. But it might be interesting to compare the "adapted" story in your book with the original version on the internet.
The grandfather in this story is portrayed as a stereotypical crotchety/cranky/grumpy old man. He has had a lifetime of experience, and, in his opinion, much of the "knowledge" found in books is nonsense compared with the practical lessons of life. So he frequently tells people that when they read some ridiculous idea in a book, the writer (of that book) is a fool, is a dreamer, has no experience with his subject, etc.
But it is interesting that in the online version, the three examples of Grandfather's statement start out with the expression, "When you read in a book ...", not "You will read in a book ...".
So I think the whole issue of the future tense (you will read ...) has been introduced by C.G. Draper while he was adapting the story for his collection of stories. I don't know why he used that tense in these sentences when he is talking about a conditional situation (not a definite occurrence of the future). Maybe he thought that the future tense was easier for beginning language students to understand than Saroyan's "when" clause? 
In any case, what Grandfather means with his remarks about books is that you can't trust the truth of something just because some "scholar" has written it down in a book. "When you read in a book ..."; "if you read in a book ..."; "Perhaps you may read in a book ..";  or as C.G. Draper expresses it, "You will read in a book ...", it doesn't matter: book authors don't know what they're talking about. [per Grandfather.]

