"The devil has been the unwilling instrument of grace..."

More from Flannery O'Connor. This is from the tail end of "On Her Own Work" in Mystery and Manners:

From my own experience in trying to make stories 'work,' I have discovered that what is needed is an action that is totally unexpected, yet totally believable, and I have found that, for me, this is always an action which indicates that grace has been offered. And frequently it is an action in which the devil has been the unwilling instrument of grace.