A Good Man Is Hard To Find What Does The Ending Mean?

At the end of Flanelly O'Connor‘s short story, the grandmother says to the Misfit, “Why you’re one of my babies. You’re one of my own children!” She reaches out and touches him on the shoulder. The Misfit suddenly springs back and shoots her in the chest three times. Then he puts his gun down and cleans his glasses. This is the story’s climax, and the Grandmother’s “moment of grace.”
The ending of A Good Man is Hard to Find causes some controversy in interpreting its meaning. O'Connor wrote the story with a particular understanding of the ending in mind, and it's an understanding that comes from her Roman Catholic worldview. What happens to the grandmother when she reaches out to touch The Misfit is called a "moment of grace" in Catholic terminology — a special kind of gift from God, in which God suddenly fills her with almost supernatural love and understanding. That enables her to see The Misfit as a fellow suffering human being whom she is obligated to love.
The grandmother realizes that she does in fact love The Misfit just like one of her own children. O'Connor presents both the perception of The Misfit as a fellow human being, and the sudden but real feeling of love for him, as gifts from God. From the Catholic worldview, the grandmother, as a human being is inclined towards evil, pettiness, and selfishness, so could never have come to feel such love without God's help.
This moment of grace is hugely important in the story. The Misfit kills the grandmother, recoiling from what seems so foreign to him, but the grandmother has already had her moment of redemption. She's grown at the moment of death more than she ever did before in her life, and dies with a peaceful smile on her face.