I actually bought Sister Emmerich’s book, specifically because I knew that it was the source Gibson used for the movie…It is a very interesting (& inspiring) read.
It is not as though that her visions were somehow “snuck in” to the movie. She has been openly acknowledged as having been a major inspiration for The Passion film.
Every book about Christ (or for that matter, any historical personage) is going to, of necessity, include some material from somewhere, other than the Gospel records, in order to have a smooth moving narrative…As such a source, the meditations of a devout believer such as Sr Emmerich are surely a better choice than the fevered imaginations of a group of writers who have never even read the NT…So, just on those grounds alone, I think her book was a good choice.
Now, if someone were going to argue that, somehow, the movie is a

better source of knowledge than the Bible, **that **would be a major, problem…
Mel Gibson, in interviews has pointed out that the real source of the story–the Scriptures-- is:thumbsup:

“readily available”.