What does the Man in Black try to achieve with the boy in 'The Dark Tower' (2017)?

I couldn't get into the film, I will buy the books.

Cookie Bean, Open the gates of Hell sound frightening; the Bible reads “outer” darkness, that too sounds scary. In the middle of night, pitch dark and (disoriented) you stumble around, bumping into things…I don’t know it just scary for this 68 year old.

very easy😒

ilove this movie! 😁