Thereās a lot going on in the film that lifts it above a standard āhorror movie,ā I think.
Fr. Damien Karrasās last name Blatty adapted from āCaritasā (Christian love of humanity, charity) and his first name came from Saint Damian, one of two twin priests who ministered as medical doctors (as Fr. Karras is in the movie - heās a Jesuit psychiatrist), as well as St. Damien of Molokai, who ministered to lepers in Hawaii before contracting their disease himself (as Fr. Karras takes the demon into himself to free the suffering girl, before falling to his death.) I think Jason Miller (who was best known as a playwright before appearing in this movie - he wrote āThat Championship Seasonā) gave an amazing performance.
Unlike most straight-up horror films, thereās a lot of nuance in character and relationships. Thereās a good view of the Jesuit collegiality in how Karrasās friend and fellow priest (played by a real priest, incidentally) looks after him throughout the film and gives him the last rites. The sense of foreboding in the opening scenes in Iraq, and Fr. Merrinās sense that his last battle with the forces of evil is coming. There are some really memorable characters, like Lee J. Cobbās police detective or the insulting Irish director played by Jack MacGowan (who I remembered best as the toady for Squire Danaher in āThe Quiet Manā). Ellen Burstyn did a great job showing the panic and confusion of a woman who doesnāt know what is going on or how to how to help her daughter. The relationship between her and Fr. Karras is well done - they are interested in each other, but not really sexually - they play off a mutual fascination with someone who is completely outside their usual scope of acquaintances (Hollywood film star and Jesuit priest).
Often overlooked is the place the Eucharist has in the film - after Fr. Karras goes to see his mother and deals with his own sorrows, and before a confrontation with the possessed girl, we see him celebrate the Eucharist - and thereās a sense that he is fully involved in the moment of the Sacrament, that it is a moment of peace and strength for him between his trials, even as he fears he is losing his faith (which Blatty has said was the intent of the scene.)