What is the effect of O'Conner's use of the phrase "good country people" throughout the story?

As with much of O'Connor's work, the titles often contain
irony, and this irony is repeated in the plot of the story. The "good country people"
are not really good - Mrs. Freeman is a chatterbox that is always bragging about her two
daughters. Mrs. Hopewell, Joy/Hulga's mother, is very insistent that the Freemans are
not "white trash" - but "good country people" because certainly a prideful woman such as
herself would never have hired white trash to work on her farm.
Manley Pointer is an evil con artist who winds up seducing Joy/Hulga, and then stealing
her pride and joy, her wooden leg, so he is not "good country people" either. None of
the characters are good country people.

Joy/Hulga imagines
herself above everyone else and ridicules the "good country people" around her because
she is educated, and they are not, so she is not "good country people" either. She
fancies herself above the "good country people" but she is not. The use of this phrase
throughout the story not only has the effect of pointing out the fact that the "good
country people" are really "bad country people" but it also emphasizes O'Connor's theme
of grace, which is Biblically based. Grace is unmerited favor, given by God to sinners -
people that do not deserve it. Even though the characters in this story are not "good",
the Bible teaches that Jesus was sent to redeem sinners, not good people. O'Connor
subscribed to the Biblical teaching that "For while we were still sinners, Christ died
for our sins." This idea of grace is evident in everything she ever wrote, and in her
letters, she constantly reminded people that this was why she wrote. This also explains
why her characters are often  so "grotesque" and undeserving of grace (like Joy/Hulga).
They are the ones that need grace the most.