Walker's "A Worn Path" reveals a woman surviving against uncaring and indifferent social and political forces. No one is consciously out to get her, but the society is uncaring and indifferent. The story is only incidentally about race or rudeness or cruelty. These are just part of the package that comes with existence. The boy doesn't shoot her, and the same people in town that are rude to her also give her the medicine she needs for free. No one is out to get her, it's just that nobody really cares and nobody is really doing much to help her.
The setting, and particularly the path (thus, the title) is indicative of this, symbolic of this. The path is not out to get her, it just is. But it sure makes life difficult for her.
The setting is indicative and symbolic of the path she takes in her struggle to survive against uncaring and indifferent societal forces. Even the boy in the woods lacks motivation for threatening her. He doesn't hate her and isn't noticably racist. He threatens her just for the fun of it.
To me, the major way that the setting plays a part in the story is by the fact that it dramatizes the struggles of the main character, Phoenix Jackson.
One of the major themes of the story is how Mrs. Jackson is struggling against her society. She is given very little respect by anyone, especially the white members of society.
The setting contributes to this idea because it forces her to struggle physically. She has to overcome various physical obstacles on her way to town. This, to me, symbolizes the general struggle that is a major theme in this story.