As the family leaves on its trip to Florida, we get a glimpse of the grandmother as she sits in the car ready for the journey:
Her collar and cuffs were white organdy trimmed with lace and at her neckline she had pinned a purple spray of cloth violets. . . . In case of an accident, anyone seeing her dead on the highway would know at once that she was a lady.
Throughout the story, the grandmother, who becomes the central character, equates a person's external attributes with his or her values. In short, if someone is dressed well and acts well, the grandmother assumes that person is a good person, goodness that also implies religiousness.
When, through the series of incredible mis-adventures, the family is at the mercy of The Misfit and his colleagues, and she sees that her family--with her son, Bailey, first--is going to be executed by The Misfit's men, the grandmother tries to convince The Misift that she perceives his inherent goodness:
'I just know you're a good man,' she said desperately. 'You're not a bit common!'
One can argue, of course, that the grandmother is making a cynical attempt to keep herself alive, and she probably is, but she is also reacting to The Misfit's ostensibly kind and polite behavior--even as he orders the killing of Bailey and his son. The grandmother assumes that The Misfit's outward behavior mirrors some inherent goodness within.
After their prolonged discussion about The Misfit's confusion about Jesus--in which he appears to be genuinely troubled by whether or not Jesus raised the dead--the grandmother reaches out to him and touches him on the shoulder and says
'Why you're one of my babies. You're one of my own children!"
At his point, clearly the grandmother has had an epiphany, a religious experience, that takes her from the superficiality of her belief that people who act good are good to a true expression of empathy for The Misfit.
Flannery O'Connor once said that her fiction often showed the action of grace in territory held by the devil. In the case of "Good Country People," the action of grace occurs when the grandmother reaches out to The Misfit, a man who still hold's the devil's territory.