In this story, O'Connor, a Roman Catholic, conveys the message that rampant evil exists in the world, but that even the most flawed of us can find God's grace in the midst of it. Several literary devices advance this message. One is foreshadowing, another is irony, and a third is the highlighting of the flawed character of the story's protagonist, the Grandmother. Finally, a bit of number symbolism points to the Christian theme.
Although this story opens as a seemingly light-hearted, comic tale of a middle-class 1950s family road trip, foreshadowings about the Misfit pop up several times, acting as "shadows" that make us aware of evil in the world. In the first paragraph, it's the Grandmother, who will have the most extended encounter with the Misfit, who points out the news report about him in the paper, even using the word "conscience":
"Here this fellow that calls himself The Misfit is aloose from the Federal Pen and headed toward Florida and you read here what it says he did to these people. Just you read it. I wouldn't take my children in any direction with a criminal like that aloose in it. I couldn't answer to my conscience if I did."
Here, too, is the story's first irony: it will, of course, be the Grandmother who points her children and grandchildren directly in the direction of the Misfit. In a second irony, a commentary on how we tend to discount the power of evil, the grandson, John Wesley, says he would handle the Misfit by smacking him in the face. That won't happen: it will be the Misfit's gang that kills the boy.
The Misfit comes up again when the family stops at a diner for lunch and the Grandmother asks the owner, Red Sammy, if he's heard of the Misfit who escaped from prison. Thus, by the time we meet the Misfit, we're expecting him: O'Connor's foreshadowing has created the story's internal logic.
The ironies continue as the story unfolds. The Grandmother's attempt to escape into the past by having the family detour to see an old plantation ironically confronts them with present evil in the form of the Misfit and his gang. And irony helps O'Connor make her point at the end: in her almost hysterical fear, when the Grandmother sees the Misfit wearing her now-dead son's shirt, she confuses her son's killer with her son, leading to her moment of grace and redemption. Grace, O'Connor is saying, comes in the strangest ways.
Finally, in creating such a visibly flawed character as the Grandmother, O'Connor drives home her message that God's grace is available to all of us. From the start, the Grandmother is difficult, childish, foolish and troublemaking, clearly a trial the family endures. She's the kind of person everyone wants to strangle, and it's through her machinations—sneaking the cat into the car, manipulating the children into insisting on seeing the plantation—that she gets the family into its deadly fix—and then doesn't have the sense to keep her mouth shut. Yet she is the one chosen to experience a moment of redemption and grace that even, for a split second, touches the heart of the Misfit. It's she, the foolish one, who is able to discern God's grace in a hardened killer before he blows her away:
... the grandmother's head cleared for an instant. She saw the man's face twisted close to her own as if he were going to cry and she murmured, "Why you're one of my babies. You're one of my own children!" She reached out and touched him on the shoulder. The Misfit sprang back as if a snake had bitten him and shot her three times through the chest.
By making such a flawed woman an agent and recipient of grace, O'Connor's message becomes more powerful: anyone can be redeemed.
Finally, the Misfit's name is mentioned 33 times, the number of years Jesus is traditionally thought to have lived, linking him to Jesus' humanity and the thus the possibility of redemption, and the Misfit shoots the Grandmother three times, a symbol of the Christian trinity, as if the Misfit feels the need to destroy Father, Son, and Holy Spirit.