A story which has nothing to offer someone with no religious faith cannot have much to offer even those who do have faith. The fact that this question is asked of Flannery O'Connor at all is at least partly due to the fact that she lived her entire life in the middle of the twentieth century, at a time when religious faith, though still very common, could no longer be taken for granted, particularly among the intelligentsia. No one bothers to ask whether there is anything for non-Christians in The Canterbury Tales or Paradise Lost.
Perhaps Flannery O'Connor's greatest gift to the reader is the grandiose oddness of her characters. The stories are far more driven by character than plot or theme, prompting some critics to question whether such people could possibly exist. O'Connor's response, like William Faulkner's, was that they do in the South, adding that "anything that comes out of the South is going to be called grotesque by the northern reader, unless it is grotesque, in which case it is going to be called realistic."
Flannery O'Connor has much to offer besides religion: bizarre and memorable characters, biting wit, and extraordinary plots. However, even her discussions of and points about religion are clearly of interest to any thoughtful reader, whether or not s/he happens to have any religious faith. The discussions of theology in such stories as "A Good Man is Hard to Find" and "Good Country People" inform and illuminate our ideas about the texts and their events, whatever our religious beliefs.