This was originally the second chapter of Jacob. When Jacob concluded writing the previous chapter, he mentioned that he could write only a hundredth part of the history of his people on the plates of Jacob, and that there were other, larger plates. At the beginning of a new chapter, he appears to repeat himself and mentions that he writes little. In this case, he clarifies that it is because it is difficult to engrave on the plates. Nevertheless, he writes because “whatsoever things we write upon anything save it be upon plates must perish and vanish away.”
From the perspective of a Mesoamerican location, this statement is not only true, but observedly true in the history of the region. When the murals at San Bartolo were discovered, it was the first time that there was a significant text from Book of Mormon times that remained. It was painted, not carved. All of the rest of the texts which have been preserved were not upon plates, but rather upon stone. During Jacob’s time, it does not appear that they had begun carving texts in stone. It has been sadly true that whatsoever they didn’t write upon plates, really did perish.
When Jacob began this chapter, he essentially repeated himself from the end of the last chapter. Had he been writing this chapter right after the previous one, there would be no reason to repeat himself. It appears that some length of time had passed between the first chapter and this new one, and Jacob read at least the ending for the previous. Thinking about that ending, he wrote this beginning, which initially repeats the information as the end of the previous chapter, but which will expand upon it. The expansion comes when Jacob notes that he is writing for future generations.