Redaction: “And these are the words” may mean that Alma is introducing Yahweh’s words, or it may mean that Mormon is introducing Alma’s words from the plates. As I read the passage, the second possibility is the better interpretation. Not only does prophecy come to the prophet in his own words, but it begins: “Behold, I perceive.… ” This phrase is at home in Alma’s description of his prophetic event, but hardly what we would expect from the Lord, whose statement would have been more forceful than a perception.
The prophecy is that the Atoning Messiah will come but that the people will still fall away four hundred years later. The reason for withholding it is obvious. Given the ultimate failure, the intermediate generations may not strive diligently during their own lifetimes. Hope is a much better motivator than fatalism.
Culture: Probably Alma and Helaman understood the four-hundred-year period as sacred. The Maya calendar system gave the name baktun to the four-hundred-year unit.
One can only imagine Mormon’s feelings, copying this fatalistic prophecy, whose fulfillment he was living. Mormon would have known that his military and missionary efforts were in vain and that he was foretold to fail. What courage it would have taken for him to carry on his task!