Hunter Duesing’s review published on Letterboxd:
Director William Friedkin describes "The Exorcist" as a film about "the mystery of faith." This description is accurate and does so by addressing the struggle between faith and reason that intensified in the Catholic Church in the wake of the cultural revolution of the sixties.
Father Kerras (Jason Miller) is a priest with a modernist outlook and attitude, informed by his background in psychiatry, which erodes his faith in God. He sees everything supernatural as something that can be explained away. When he encounters a demon possessing a little girl named Regan (Linda Blair), at first it seems like mental illness, but it soon becomes apparent that the Devil himself is at work. There is a scene where he celebrates Mass, and the reality of the body and blood of Christ dawns on him once again. He sees the miracle of Jesus coming down to the altar. The priest who we contrast with Kerras is Father Merrin (Max Von Sydow). He reminds me of the elderly priests I know in the Priestly Fraternity of Saint Peter who've been around for over sixty years. He knows the faith, he knows God exists, and he knows not only that Heaven is real, but Hell is also real. There is no question. His faith is solid.
"The Exorcist" addresses a modern world where holy mystery is replaced with obsessive rationalism, a rationalism that the Catholic Church was not immune from. Friedkin and writer William Peter Blatty remind us of the mystery of faith in this film's encounter with evil. It's as powerful today as ever.