I recall a short while ago (though I am unable, for reasons unknown, to locate the thread to which I am referring) a discussion debating whether Karras or Merrin was the “real” Exorcist of the novel/film. I just came across this interview with Blatty that confirms it:
http://www.gadflyonline.com/archive/October98/archive-blatty.html
The book and film are both titled The Exorcist. Who is the primary exorcist—Merrin or Karras? If it is Karras as I suspect, is the character of Regan really just a side story?
You’re right, the exorcist (of the title) is Karras. And Regan’s possession is the crucible of his struggle for faith, his salvation.
Conversely, it is not as clear in the movie that Karras is the exorcist of the title as it is in the book.
I think this is an audience mis-perception problem. It’s all there. It’s clear.
If this is indeed the case, why add a clip of Merrin following every phrase of “The one hope. The only hope. The Exorcist” and the like?