Most of the story is told from Connie's point of view. We learn, feel, and get confused about things at the same time she does. Since much of the story is restricted to her perspective, Arnold Friend remains mysterious, evil, and utterly creepy.
A great example of this narrative point of view is the scene in which Connie is so paralyzed with terror that she can't bring herself to call the police (144). We're told that she is "locked" in a "noisy sorrowful wailing," but the image is confusing—how do you get "locked" in a "wailing"? —that it's impossible to pin down exactly what's going on. Our confusion as readers helps us feel Connie's terror.
On the other hand, using the third person (rather than letting Connie tell the story through her "I") gives the narrative enough distance to move beyond the narrow circle of her consciousness and lets the story move to a more general, almost allegorical level. Thus, when Connie sees the "vast sunlit reaches of land," the story is not only giving us her visual hallucination, but also inviting us to think about the deeper symbolism of "sunlit reaches of land."