Here's why it was so effective:
* Eerie and haunting: The song's repetitive, minimalist melody and use of unusual instruments creates a sense of unease and dread.
* Thematic resonance: The music's gradual build-up and unexpected shifts in tone mirrored the escalating horror and demonic possession experienced by the protagonist.
* Emotional manipulation: The song's melancholic and unsettling nature effectively heightened the emotional impact of the film's most terrifying scenes.
Friedkin initially wanted to use another piece of music but was convinced by the record label to give "Tubular Bells" a shot. The rest, as they say, is history. The song became synonymous with the film, making it one of the most recognizable and influential pieces of horror music ever written.