In a deleted scene which appears in the (terrible) Version You’ve Never Seen there’s a conversation between Karras and Merrin on the stairs in which Karras asks that question. Merrin’s answer is that the demon selected an innocent young girl so that it could defile something pure and make everyone despair that God could not possibly love us.
There’s another factor. The demon seems to want to square off against Father Merrin. They ‘met’ in Iraq at the beginning, and the demon could be the same one he exorcised in the past. It even yells ‘MERRIN!!’ when he arrives as the house. The demon tormented Karras with images of his mother so that Merrin would tell Karras to ‘get out’. Unfortunately he obeyed, allowing the demon to kill Merrin, which seemed to be its goal.
It’s interesting to note that the exorcism actually
fails
. What succeeds is Karras’ Christ-like sacrifice - he takes the demon into himself and then commits suicide to destroy it and save Regan. He had previously lost his faith and failed to ‘save’ his mother, at the cost of his life he regains his faith and saves an innocent girl.
The Exorcist is so much more than a horror film, Friedkin has said it’s about ‘the mystery of faith’, these deeper concerns are what make the film an endlessly rewatchable classic, with many Catholic fans. I’m not religious but it gets me pondering the value of faith, and the presence of evil in today’s world (more on this here:
https://www.filmboards.com/board/p/22873798/permalink/#p22873798
)

Is it hinted in the first movie that she kind of has esp.
Welcome to Filmboards. The short bus of movie chat forums.

You didn't read the source material, obviously. It wanted choirboy-revenge on a priest.

This. And it wanted to corrupt the soul of a child because it thought doing that was the coolest thing in demon world.

Because she was playing with the Ouija board, and so it could get to Karras
Melton1 Wanted for Pedophilia:
https://i.ibb.co/6cnPmJVr/IMG-0830.jpg
https://m.youtube.com/shorts/Zjxk307CND0

𝙽𝚈𝙲 []

No. That movie sucked you perv.

Watch Part II: Heretic

“Call a SPADE, a SPADE; and a TRANNY, a TRANNY, or an IT!!!”.
"THAT'S SOME BAD
SHIT
,
HARRY
!".