O'Connor often ues both humor and violence in her stories, managing to combine those traits with a deep moral and religious seriousness. "Revelation" is no exception.
Perhaps the moments in the story when violence and humor come together most forcefully are the moments just before Mrs. Turpin has the book thrown at her (literally).
Just as Mrs. Turpin is congratulating herself on the good fortune of being Mrs. Turpin (thus illustrating one of O'Connor's major themes -- the theme of pride), she is hit with the appropriately titled book Human Development. All throughout the first part of the story, Mrs. Turpin's pride has been consistently humorous. She takes herself so seriously that O'Connor's readers find it difficult to take her seriously at all. She is a walking, talking demonstration of the follies of pride (but also of its serious moral failings), and much of what she says is quite unintentionally funny (unintentionally on her part, but intentionally on O'Connor's).
Her pride is so humorous that it makes us laugh, especially when she thanks Jesus for making her exactly who she is (with no room for improvement, in her opinion). She also thanks Jesus for giving her exactly the kind of life she presently enjoys (again, she can't imagine anything better, which suggests the poverty of her imagination). "For one thing," O'Connor writes, "somebody else could have got Claud" -- a funny line in a story full of funny lines. Claud, after all, is not exactly Paul Newman, but he is the perfect husband for Mrs. Turpin because she dominates him so easily.
Immediately after Mrs. Turpin thanks Jesus once more, O'Connor writes as follows (and with no transition):
The book struck her directly over her left eye. It struck almost at the same instant that she realized that the girl was about to hurl it.
The abrupt shift -- from the name of Jesus to the attack by the girl (ironically and humorously named Mary Grace -- a name with definite Christian connotations) is typical of the way O'Connor combines humor and violence. The attack itself is somewhat funny; the fact that the attacker is named Mary Grace is funny as well; the fact tthat the book is titled Human Development is funny; and the fact that O'Connor surprises us just as much as she surprises Mrs. Turpin is also funny.
At the same time, the attack has serious implications. O'Connor would have seen it as a means by which God attempts to offer Mrs. Turpin grace, if she will only accept it. O'Connor also would have suggested that this is indeed a moment that may lead, if Mrs. Turpin responds properly, to real human development. Thus, in her typical way, O'Connor manages to be combine humor, violence, and deep spiritual seriousness.