One of the benefits of Jackson's third person narrator is an objective narrator. Since our unnamed narrator is speaking from the outside of the story (as an observer of the events as they unfold) the narrator is able to objectively lead the reader through the town's unusual annual event.
At the end of the story, when the papers have been drawn, and the "winner" decided, the narrator points out:
Although the villagers had forgotten the ritual and lost the original black box, they still remembered to use stones. The pile of stones the boys had made earlier was ready; there were stones on the ground with the blowing scraps of paper that had come out of the box Delacroix selected a stone so large she had to pick it up with both hands and turned to Mrs. Dunbar. "Come on," she said. "Hurry up."
While the audience may be horrified to watch the friend turn on Mrs. Hutchinson, the narrator offers no evaluation of the characters choices, only exposition on their movements. The narrator's calm and nonjudgmental tone add to the shock of the story's events. The reader grows more and more disturbed not just by the horrific events, but by the causal retelling of them, as though this even could happen at anytime in any city.