Mystery and Manners: Occasional Prose is a critical work, a collection of essays written by Flannery O'Connor about her own writing. She explains her approach to fiction, her concept of literature, etc. Her comments on her short story A Good Man is Hard to Find attempt to explain the gothic nature of her fiction. She says that in this story, she attempts to address:
"the action of grace in territory held largely by the devil"
The grandmother offers grace to the Misfit when she reaches out and touches him just before he kills her. In this way, she feels she can evoke the "mystery of Christianity." O'Connor was a strong Catholic and her writing reflects her deeply held religious beliefs. However, the stories themselves are so deep that one really needs a knowledge of these Catholic beliefs to fully comprehend her stories. She tries to evoke her themes, she says, in extraordinary ways by the plot of this short story. She says that critics of this short story often label it grotesque, but in her defense, she says:
"anything that comes out of the South is going to be called grotesque by the northern reader, unless it is grotesque, in which case it is going to be called realistic"
She rejects accusations of racism in her story (the use of the "N" word, etc.) but explains that her story is set in the South and racism is a part of life there, not that she is endorsing it - just representing it. I love this quote by her - it applies to all of her "unique" characters, including the Misfit and the grandmother, in my view:
"Whenever I am asked why Southern writers particularly have a penchant for writing about freaks, I say it is because we are still able to recognize one."
Read about the story here on eNotes.