The first person narrator adds mystery to the story because we only have John’s perspective, when a third person omniscient narrator would tell us what everyone is thinking.
John is the narrator of the story. The first person point of view is used because John describes only what he thinks and feels, using “I” and “me,” for example. If the point of view were third person omniscient, it would use “John” and “he” and we would know what the other characters are thinking and feeling too.
As John takes his journey, we are always only in his head. We only know what he tells us. For example, when he has his vision and leaves on his quest, we only know what his father says and what John thinks he feels.
"This is a very strong dream," he said." It may eat you up."
"I am not afraid," I said and looked at him with both eyes. My voice sounded thin in my ears but that was because of the smoke.
We do not know what his father really feels. Also, if we had a third person omniscient narrator we might be told that John is really in a future version of my world, and know he was in New York sooner. Thus, having John tell the story adds mystery and suspense.