Complex sentence: Author David L. Barr in his book "The Reality of Apocalypse", says Revelation may be the most violent book in the entire Bible, and that it has been used to justify Christian hostility, Christian imperialism and Christian sectarian violence.
Split into simpler sentences: Author David L. Barr in his book "The Reality of Apocalypse", says Revelation may be the most violent book in the entire Bible. Barr says the Book of Revelation has been used to justify Christian hostility, Christian imperialism and Christian sectarian violence.