How does having a narrator like Jim aid in telling the story?

Jim's narration adds a lot to the novel. First of all, he's a young man, and that gives us a narration which embodies two different themes. Treasure Island isn't just an adventure story; its a narration about growing up as well (coming of age).

Jim's narration also gives us a more accurate picture of what's really going on. To see things through the eyes of a child is to see what is real. He records heroic acts for what they are, and he tells them modestly and humbly. There's no exaggeration in what he writes. Every moment is a learning experience, and because of his youth, Jim doesn't hesitate to take responsibility for his own mistakes, doesn't make excuses for them, and has no problem admitting to fear, indecision, or regrets over the events that take place. His narration is truthful; he doesn't have to tell the story about the "fish that got away," or something "that almost was." He has no need to embellish his stories because of his age......... he hasn't lived all of his "stories" yet, so what he see and speaks of are exactly what he sees.