The mother's argument to her son is that he should view the world in terms of spiritual energies, like demons and ghosts are literally haunting us in unseen ways. An interesting thing happens when the reader decides to take her suggestion and view the novel as a ghost story.
Suddenly, we see that Eddie (a named character) means more to the boy (an unnamed character) than just family trivia. It's as if the boy is being haunted by Eddie's ghost, because the boy experiences a spiritual conviction about Eddie's death, eventually discerning that Eddie was innocent. Perhaps the reason the Eddie's legacy haunts the boy is that his family doesn't want to talk about it, which means that Eddie's legacy is in jeopardy (which is a common theory about ghosts, that they return to help manage their legacies).
Regardless, the boy learns that his family is not the safe-haven he thought they were. Not only do they not help the boy in defending uncle Eddie's legacy, they also pester him for his curiosity, showing the boy that the family has already rejected Eddie in a way. He decides that they also have rejected him, and this, combined with the mental delusions of his ill mother, help the boy to achieve a religious breakthrough.
He realizes that his mother tends to view the world in a very specific way, and that he has adopted her way of thinking about God and religion, but actually, he can find one that fits better. For a moment, he is captivated by an existential dilemma: He realizes that everyone has their own unique take on life, religion, and God, a realization that simultaneously matures him and disappoints him, because he realizes that he was given a false sense of security by his mother's avid religiosity. This helps him to see that perhaps, the family is not to be trusted, not about religion, but also not about uncle Eddie.
