There is some quite good worldbuilding in this story, as well as probably the best representation of what it would be like to live in a post-apocalyptic world that I've ever read, but alas some elements in it are just too on the nose, and too preachy to ignore.
Especially the ending.
And all the god talk.
And the child being practically called mini-Jesus by his father.
I get it, it may be one way to cope with (the never really revealed) end of civilization as we know it, but still. It's too forced for my taste. Especially at the end where the father outright tells his son to pretend to talk to him after he's dead, pretend really hard and then he'll talk back. I'm sorry but that's not ok.
But who knows, maybe that was the whole point of putting it there. But if an author telling a story from a third person's perspective can't get it through to the reader if this is just a delusion of the character, or the actual moral of his story (the good guys aka those who believe in god, I'm sorry, who pretend to talk to god aka a dead guy and actually believe that the dead guy talks back, just because they really want to), well I think that deserves a few less stars that a story that is actually understandable by anyone besides the author.
Maybe I'm expecting too much but I would think that's a basic requirement of a novel, or of any good story: to at least try and get a point across to the reader or audience, instead of just spouting a few long and a few nice descriptions and metaphors but at the end still keeping the moral or the essence of the story to yourself.