First, this is unquestionably the most terrifying book I have ever read. Secondly, many readers seem to enjoy the book but miss the point. I find it amusing that many hard-core Christian types are down on this book (i,e, it glorifies Satan, etc.), as that shows that they clearly do not know anything about it. The entire point of the book is that a priest, trained in the ways of science (he is a Psychiatrist) has through his pursuit of science lost his belief in God. His lack of faith in God brings with it a disbelief in the existance of Satan as well. When he is asked to see the possessed girl, Regan, it is as a priest, to confront what is clearly (to the mother) a case of demonic possession. Instead he approches the situation with his scientific rather than his spiritual training, and sees the girl as insane and thus treatable via science, rather than possessed. Even in the face of all evidence, he steadfastly refuses to admit that there is anything supernatural about the girl's condition, though science has so far failed miserably to treat the girl. We get insight into this when he arranges a exorcism (for cathartic, not spiritual, reasons) and interacts with a priest who is a believer, has performed exorcisms in the past, and is very respectful and afraid of the power of a very real Satan. At one point, the young priest discusses the possession of Regan, and tells the old priest that he cannot understand what Satan might stand to gain from harming an innocent girl. The old priest replies that in a possession it is not the possessed who is the target, but rather the persons around the possessed. Upon hearing that, and upon hearing some very personal attacks on the young priest by the possessed/insane Regan, it becomes obvious that the young priest is the target of Satan's attack, and the priest's lack of faith is what has made him a target. Later, after the death of the old priest, and upon the occurance of some shocking and blatantly supernatural occurances, the young priest comes to believe that the girl really is under possession by Satan. At that point, the logic is obvious. If Satan exists, then God must exist also, and this brings a sudden reawakening of the young priest's faith. This gives him the strength to spiritually combat Satan and defeat him, and thereby rescue the girl. So, the point is that the priest has lost his faith to science, and is not able to effectively counter Satan until his belief in God returns. Thus Heaven triumphs over Hell, and I really can't understand why this would be lost on the many naysayers who have tried to steer people from this shocking book. One wonders who is truly the pawn in the plot of this book; Regan, in Satan's attack on the young priest; or Satan himself, in some heavenly strategy to bring the priest back into the fold. Note that I have deliberately oversimplified the story line so as not to ruin the book for those who have yet to read it. Be forewarned that the book is complex, shocking, graphic (violence and perverse sexuality) and is terrifying, but you will not find a better horror novel anywhere. I can't recommend this book highly enough, but it is not for the faint hearted. I also find it noteworthy that after at least five reads of the book, I (a thirtyish man) still find it necessary to sleep with the light on for a few days after finishing the book