In "By the Waters of Babylon" what is the significance of the journey to John and his people?

On his journey, John makes the highly significant discovery that the Place of the Gods was just a city, and that the Gods themselves weren't actually gods; in fact, they were men, just like himself and his people.  This shatters all of the myths, taboos, and many cultural beliefs of his people.  A lot of their existence centers around those mythical "gods" and the strict rules concerning their dead places and the great burning.  John realizes, on his journey, the significance of this discovery.  He states, "It is a great knowledge, hard to tell and believe."  He also realizes while he was there that despite the "great magic" that these people had (all of the technology), it didn't keep them from total destruction.  This puzzles him, but after his father's wise advice, John realizes that perhaps it is because "they at knowledge too fast," which means that they used advancements but left behind the wisdom necessary to wisely use those advancements.

John, through the advice of his father, decides to relate the truth of the situation to them a bit at a time, slowly, so that they can fully understand it, and use it well before learning more.  They start with gathering books and learning from them, and he hopes that as they do this, they can "make a beginning."

John's journey leads to incredible discoveries that will change the lives of his people forever, hopefully for the better as they learn from the mistakes of the past.  I hope that those thoughts help a bit; good luck!