3. At the end of the story, John’s father tells John, “Truth is a hard dear to hunt. If you eat too much truth at once, you may die of the truth. It was not idly [for no good reason] that our fathers forbade the Dead Places.” What do you think his father means by this statement? What advice or warning is he giving to John, the future leader of the tribe?

The quote from John's father is basically telling John to be careful with the truth.  John has learned that the great city that he explored wasn't inhabited by gods.  It was inhabited by normal men and women like himself.  They were powerful and knowledgeable, but they were still ultimately destroyed.  John is so amazed by what he discovered that he wants to tell his people the truth about what he has learned.  John believes that the truth will be a good thing and a good thing only; however, his father tells him that the truth might also be trouble as well.  Food is a good thing, but if you eat too much of it, you can die.  That's what John's father is saying.  The truth is good, but knowing too much can be harmful. That's why the saying "ignorance is bliss" has a lot of truth to it.  John's father is warning John that knowing the truth could be incredibly dangerous for the people.  For generations they have believed in a certain "truth."  John's reveal would destroy all of that, and it could shake their society to its very foundations.  That is a dangerous thing.  
John takes the warning to heart and realizes that his father is correct.  John decides that giving his people the truth is still the right move, but he decides to do it little by little.  That way it doesn't shake things up too much too soon.  

He was right—it is better the truth should come little by little. I have learned that, being a priest. Perhaps, in the old days, they ate knowledge too fast.