While promoting the film on The Late Late Show with Craig Ferguson (2005) (airdate 8/29/12), Jeffrey Dean Morgan reported that strange incidents took place during production that couldn't be explained. Lights exploded during the filming of key scenes, and just two days after wrapping principal photography, all of the props for the film, stored in case of re-shoots, were destroyed in a fire that mysteriously erupted from within the storage-house.
The book that the father brings into the house and reads at Emma's bedside is the ArtScroll/Mesorah edition of the Tenach (Jewish Bible = Old Testament), first published in 1996, and he is reading from the English translation of Psalm 91. That edition follows the Orthodox affectation of using "HaShem" (literally, 'THE Name') where most other English versions have "The Lord"; the same substitution occurs in the Hebrew prayers recited in the synagogue and exorcism scenes.
Was originally rated-R by the MPAA for "violence, terror, and disturbing images" but the film was eventually edited to receive a PG-13 rating for "mature thematic material involving violence and disturbing sequences".