In studying Nephi’s vision, it seemed to me that I should mark which parts were vision and which parts were angelic exposition. 

In doing so, I noticed that the angel put a lot of effort into describing the Bible and the scriptures among the Gentiles.  I wondered, why was all that needed?  I looked at what Nephi had seen prior to it, and I realized he had seen something very odd from a spiritual standpoint.  He had seen the formation of a great and abominable church, and then he had seen gentile nations conquering the promised land while carrying a book and that they had the Lord’s spirit!  This would be puzzling.  Nephi would ask himself how a people with a great and abominable church among them could be permitted to prosper so and be favored over his own people who had dwindled in unbelief.

The answer was that the book (the Bible) had influenced the gentiles for good, even after it had been corrupted by the great and abominable church, and even though the corruptions caused lots of mistakes.  The book was more powerful than the great and abominable church.  The angel wanted Nephi to understand the exact nature of the book and where the gentiles’ blessings came from.