Flannery O'Connor's fiction is about revelation: does the cruelty of the physical world reveal God's grace? The presumptive answer seems like it should be "no": her stories are horrific; God seems to have abandoned the world. But, if you look behind and beyond her fiction, you will see a world where God works in mysterious, if not benevolent, ways.
Remember, O'Connor writes comedy (of the divine sort). And she uses indirect storytelling to suggest her overall aims. In this way, O'Connor's work is confusing, because she gives us more of what she doesn't believe than what she believes. We have to intuit her thesis and her characters' motivations. Believe me, even the best of her readers are, at one time or another, confused. Even the title suggests that we will have difficulty "finding" her "good man" (Jesus).
Here are some presumptive questions that O'Connor is asking us in "A Good Man is Hard to Find":
Does the grandmother really have a moment of revelation before she is shot? Does her revelation trigger a revelation in the Misfit? Does she realize that her "once saved always saved" mentality has served her wrong? Does she acknowledge that her self-righteousness is as bad a sin as the Misfit's murders? Should we live every day as if we had a gun to our heads?
If you read the story closely, the explicit answers to these implicit questions are, of course, "yes."