The Exorcist was part of a wave of filmmaking in the 1970s where auteurs took over from the studio system, and there are many classics from the period resulting from the change. Woody Allen made Annie Hall, we got The Godfather series, Taxi Driver and Alien at the same time. Then there was the climactic tour de force that was the Star Wars franchise.
Film for a while was something made as art, and even in horror the Baby Boomers asked bigger questions. The Shining was about men turning violent because of the pressure of having to provide (as well as a haunted house story). Hallowe'en looked at the fear of domestic violence and rape between siblings and was the first slasher film. The Amityville Horror was about the fear of buying a house that was an unsellable money pit.
The Exorcist started out as a book by William Peter Blatty and it looked at religion.
If you look at horror films in the 1950s and before, the supernatural played a large part. Vampires, witches, Satanic possession, condemnation to Hell. But with church attendance falling off, Boomers becoming much more free-spirited and bucking the social and religious conventions of their parents, and so forth - horror became remarkably atheist. You weren't worried about eternal torment in Hell anymore, if anything you were worried your child would turn out to be a literal monster, or that your house would turn out to be an unsellable, constantly breaking down money pit. The Boomers had also gone through the ringer of trying out different religions on - Hinduism, EST, cults of all sorts. And they'd found there for the most part not personal liberation, but hucksters and in the case of Charles Manson, a very dangerous and murderous cult of personality.
From this point on, there are spoilers
The Exorcist was a very very scary film in its day - because it was about losing your religion at a time when people were. Modern atheists like Jimmy Carr or George Carlin would have just scoffed and said "gullible stupid idiot, religion isn't real, here's a highly offensive joke about Christianity, hurr durr Christians are stupid." At the time, however, people did still have one foot in ther old beliefs - with some residual fear. And even some ex-muslims I know who have been convinced utterly academically of the falsehood of Islam, don't attend mosque and don't pray still have elevated heart rates and a tang of fear in their mouths when they eat pork. There's a sort of Pascal's Wager that plays out in situations like this, and America was in the partial grip thereof.
It was also scary because they used a whole host of technologies to amplify the horror. Most animals feel agitated and panicked when they hear the angry buzzing of a bee's wings - not in flight, but the warning buzz they make with them to scare off potential attackers. The filmmakers put a bunch of bees in a jar and shook them violently for a while until they were in a killing frenzy, and then recorded the buzz. They then pitched it down by slowing the tape, and put that sound underneath key scenes. They lowered the temperature in theaters during certain times. But they profited most from a device called a tachistocope which shot images and text at subliminal levels onto the screen while the movie was playing. Research had shown that "YOU ARE THIRSTY" overlaid over a screen made people buy a lot more drinks, which is why the use of such devices is now illegal. Overlaying messages that you are going to die and you are going to be in eternal pain made some people run screaming from the theater, vomiting in panic. Some vestiges from these techniques can be seen in the home video version where a leering death's head flashes for a few moments in lieu of a character's face in a scene or two.
But even though the modern experience is a sort of blasé, trick-free story aimed at an audience that's already flown the coop, the story's a good one - and for those in religion, there are some fantastic themes therein, which I will bold from here on in.
The movie opens with Father Merrin, an exorcist in the Catholic church but also an archaeologist. While on a dig in Iraq, a runner excitedly tells Merrin that they've found relics not from the period interspersed with the other relics in the dig. Merrin goes to investigate and finds a statue of the Yezidi God (and Satan himself) Pazuzu, whom Merrin barely defeated in an exorcism some years back. Merrin realizes that this is not a mere coincidence, but a message from Pazuzu to him that he is back. Merrin resigns from the dig, making his decision while using tea to take the heart medication he now requires to stay alive - and heads back to America.
Meanwhile, an actress living in a rented house in Georgetown is having some problems with her rented house. There are noises in the attic, which the housekeeper assumes is rats. Also with her just-turned teen daughter, who recently started to talk to an entity called Captain Howdy on a Ouija board.
Meanwhile Father Karras is a psychiatrist and a Catholic priest. He's trying to get his aged mother to move out of New York City but she refuses. In her cold, run-down tenement building, she assures him she's fine, and he assures her everything is alright with him, but he's having huge doubts about his faith and wants to be reassigned. It kills him to go back to DC away from her, but he does.
At first the actress' teenage girl, Regan, wanders in to a Hollywood-elite party sleepwalking and confused and urinates on the spot while standing there confused. Her behavior becomes even more erratic and confused, and strange changes come over her body. "Help Me" shows up in raised welts on her skin, she starts talking in odd voices. She kills the director on the film the actress is making by hurling him out the window. One of the guests at that party is local priest Father Dyer, whose parish has seen the statue of the Virgin Mary vandalized by being desecrated with blood, which leads to the church later getting involved.
At first they try a series of painful spinal taps and other medical tortures, her screaming as they line an imaging window over her forehead (the target of same lined up on her forehead being reminiscent of the sign of the cross on the forehead done on Ash Wednesday and at baptism. But medical science has no idea what is wrong with her.
Karras' faith is shaken and he no longer believes in God after his frail old mother dies, cold and poor in New York. Before her death she was hospitalized for edema on the brain, confused and scared in a psychiatric ward. "Why are you doing this to me, Dimmie"? she asked him with noncomprehending eyes. She pointed out to him multiple times that as a doctor, he'd have had enough money to look after them both but for him having taken a vow of poverty as part of the Church, and those words weigh heavily upon him after her passing. Karras is going through the motions, boxing in the church gym and taking on his case load, but he wants out. He has a disturbing dream of his mother looking over at him in a New York subway station, and then descending a flight of stairs into the earth. Father Dyer visits Karras and hears this impromptu confession and offers impromptu pastoral care with a bottle of liquor and the assurance there was nothing Karras could have done to save her.
Medical science is failing both Karras and the actress.
Regan's behavior becomes more erratic. She screams in an inhuman voice "The Sow is Mine!" and then spreads her legs at the medical staff, urging them to "Fuck me! Fuck me!" The mother demands answers from the doctors, who mutter some inconclusive and non committal stuff about "chemical imbalances" before ducking out. Karras gets involved, first as a psychiatrist, then as a priest - even though he no longer has any faith. A recording taken of her talking is sent to a university linguistics department to determine what language it's in. The lab angrily snaps back that they have no time for jokes - it's actually English, but backwards.
In an oft-parodied and memorable image, father Merrin shows up in his trademark hat under a street lamp after Karras decides it's time for an exorcism. Neither he nor the mother have any real faith in God - earlier in the film the churchmen sort of angrily point out to her that they're there as day-in, day-out counsellors of faith, not one-shot exterminators and pest control. But the mother is truly desperate as Regan has clearly decayed physically and mentally. Karras, from a medical perspective, points out that she is actually dying. Merrin wonders if she can be sedated, but Karras rules that out, saying it would probably kill her.
They set about the actual exorcism. Karras tries to intellectualize it, pointing out from his notes a clear case of multiple personality. Merrin quietly states there is only one. Merrin prepares for a last stand, his own health failing him, and warns Karras to not listen in any way to the Devil. He points out the reason for all of this is to spread despair, to get people to stop believing that God loves them. He has a target here, and it might not be obvious. So don't listen to anything being said, carry out the ritual, and focus on God's love and power instead.
From the film: "Especially important is the warning to avoid conversations with the demon. We may ask what is relevant but anything beyond that is dangerous. He is a liar. The demon is a liar. He will lie to confuse us. But he will also mix lies with the truth to attack us. The attack is psychological, Damien, and powerful. So don't listen to him. Remember that - do not listen. "
That's all the Devil has ever been about. Despair, pain, lies, guilt. He only has power in this world, but his true target is the next.
From the film: "I think the point is to make us despair. To see ourselves as... animal and ugly. To make us reject the possibility that God could love us."
They start the ritual, and Regan snarls in her new inhuman voice at them both. She calls Merrin a "faggot" and taunts them to engage in anal sex. A momentary flash of annoyance from Merrin, and a faceful of holy water is his response, which causes slash-like burns. (We get hints from this what Merrin's own dark secrets are). They go through the ritual motions and the Devil, unable to distract them with personal attacks, causes the ceiling to crack, Regan to levitate off the bed, and the room to go glacially cold in an attempt to get them to stop. (The actress playing the little girl, Linda Blair never voluntarily went anywhere cold again, and in fact moved to Florida to the hottest part of the country she could find, having a lifelong aversion to cold temperatures).
The Devil begins to go after Karras. Attacking him on his guilts (he impersonates Karras' mother asking him "Why did you do this to me, Dimmie? So cold, with the roaches, and the rats") and his fears (Karras is concerned his mother ended up in Hell, that his dream meant she had gone there, and the Devil taunts him with "your mother sucks cocks in hell"). Merrin is concerned that these are starting to affect Karras and orders him out of the room.
Karras returns to find Merrin lifeless. The devil laughs in triumph, and even more so at the pain this causes Karras. Whereas Merrin defeated Pazuzu earlier, Pazuzu has evened the score. With only the inexperienced Karras present, the situation is literally hopeless. In pain, anguish and despair Karras begins physically assaulting Regan, screaming at the Devil with the only gambit he has left. "Take me instead!" The Devil HAPPILY takes that offer, Karras was the target all along. Karras' physical form changes as Regan begins to return to normalcy, sobbing in pain in the corner. Before the Devil can completely take him over however, Karras leaps from the same window that Regan threw the director from, resulting in fatal injuries. But, proving that the Devil does not have the final victory, Father Dyer is one of many who comes across Father Karras' dying body, and does the absolution, confession and Last Rites.
Life returns to normal in Georgetown, the horror has passed. Regan has no memory of any of this, and with it pretty clear that she was non compos mentis at the time she killed the director of the movie, and from a legal perspective only temporarily insane - the police file on the case has been closed. The priest Father Dyer and the police lieutenant who'd been investigating the case agree to take in a movie together as friends, and to work closer together in the future.
The interesting thing is, the movie could have even been more horrific. Tubular Bells was used in the soundtrack - but was more of a mournful New Age piece. After scoring the film, the director William Friedkin came across out-there electronic pioneers Tangerine Dream and asked them to come up with a horror soundtrack for his next film instead. If you listen to the soundtrack for Sorceror and imagine how that would have worked with The Exorcist, you get a truly, truly dark collaboration.
It was followed by a series of terrible sequels and at this time is about to be made into a TV series, which will probably focus like the ensuing films did on action, jump scares and supernatural porn, as opposed to the very real and dark messages in the original.
Please find the film, and/or the accompanying book, and watch it prayerfully - even if you are atheist. It's a dark film and an uncomfortable one and filled with shocking images and even more shocking ideas. But to some of us, the themes in it are very, horribly real.