A great deal of O'Connor's characterization has, obviously, to do with her own approach to life and her search for meaning through the relatively difficult portions of her life.  They are described as:

souls torn between heaven and hell, looking for solace in self-willed religion or high-handed and vain intellectualism.

This idea of a character that cannot quite find its place and at the same time is looking for comfort in a religion that is not exactly taught by external teachers or pastors but one that is constructed using pieces of that external religion to build ones own is common in her work.

The second type of character is interesting because in some ways it is in contrast with the other common character in that those who turn to intellectualism are often seen as vain or somehow empty by those who have turned to religion for life's answers instead.