What does John's father tell him about his dream? What do these words reveal about the reason it is forbidden to travel east?
On the surface, John's father says very little about the dream, and his words seem to send a mixed message: John should follow his intuition about the dream, yet remember that travelling east is forbidden. It is forbidden because travelling east brings one closer to the Place of the Gods, the place from which people are "most strictly forbidden" to go.
But before this scene, the narrator has provided us with crucial information that suggests John's father suspects his son may violate the taboo. He nevertheless encourages John to go, so perhaps John's father thinks his son should attempt to visit the Place of the Gods. There are hints in the narrative that John's father guesses the truth about the gods, and believes his son may be the right person to investigate further.
Before John leaves, John's father says the following about the dream:
"This is a very strong dream," he said. "It may eat you up."
These words suggest that something powerful is calling to John, perhaps something too powerful for John to handle.
Then John's father invokes the official "party line" about traveling east:
"It is forbidden to travel east . . . It is forbidden to go to the Place of the Gods."
But even as he says these words, he equips his son for the journey—giving him the bow and arrows. Does he understand that John may end up violating the taboo? Is he implicitly giving John his approval for investigating the ruined city? There is evidence for this point of view.
When John repeats back to his father that, yes, "all of these things are forbidden," he feels less than sincere. As John confides to the reader, "It was my voice that spoke and not my spirit." And John's father's immediate response is to suggest that he empathizes with whatever John is feeling:
"My son," he said. "Once I had young dreams"
The narrator has previously suggested that John's father is attentive to his son. He has watched over him, held him to the highest standards, and raised him to be a priest. He has also taken his son into his confidence, explaining that it serves the priests' interests to let the hunters think they "do all things by chants and spells," when in fact many of the priests' abilities stem from practical knowledge they have acquired from the ancient books. The common people fear the Dead Places, but priests can enter them without fear. They know these places contain useful things, like metal.
In short, we have reason to think that John's father knows his son pretty well, and may be able to detect John's true intentions. And their relationship has conspiratorial overtones. They share secret knowledge, and understand that some aspects of their religion are not to be taken literally.
So when John's father tells him that is dream is "very strong," and sends him on his way, we are left with the impression that the Place of the Gods is officially forbidden, and potentially very dangerous. But it is also worth investigating. Privately, John's father may not view the violation of this taboo as such a terrible thing.
John's father says the following about John's dream.
"This is a very strong dream," he said." It may eat you up."
In fact, he says the "strong dream" part twice. Strong dream could refer to the dream simply being a very vivid and real feeling dream. I don't believe that interpretation though based on how much spiritual mysticism is present in the story. I think John's father means that John's dream shows a truth about the gods and the Place of the Gods. I think that the father knows that the dream is going to consume John's thoughts and guide his actions. It will consume John (eat him up).
The "eat you up" line is also a veiled hint of danger. I believe that John's father knows that John will go east to the Place of the Gods. I also believe that John's father knows the trip might kill John. The city was likely destroyed by a nuclear holocaust, and radiation poisoning tends to "eat" the body. Hair loss, uncontrollable vomiting, lesions, weakness, and fatigue are all common symptoms. If John goes east to prove his dream real, the Place of the Gods might very much indeed eat John alive. That's why it is forbidden to go east. The place is toxic. But John discovers that enough time has past for the radiation levels to be harmless.