This chapter was originally chapter II in the 1830 edition of the Book of Mormon. The whole of our current chapters 1 and 2 were a single chapter before they there thematically divided. This chapter continues the blessings of the sons, and the blessing on Joseph declares that he, like Jacob, was born in the wilderness. The reason that this is a new chapter is not the change of subject, but rather the concluding amen at the end of Lehi’s discourse directed to Jacob and indirectly directed to his entire family. When the word amen is actively testifying to what has been said, it closes a chapter in Nephi’s writing. We will later see exactly the same rule in Mormon’s writings. Thus, it would appear that Nephi established this literary rule and the tradition continued for the nearly one thousand years separating Nephi and Mormon.
The birth order of the two sons and their respective names, suggest the possibility that they might have been twins. Nephi specifically mentioned that Lehi discovered, or had confirmed, that he was of the house of Joseph. In verse 4 of this chapter, Lehi specifically mentions that his son is named for their illustrious ancestor. By the time these sons were born in the wilderness, Lehi and Sariah were both older, and perhaps having a single child would have been surprising. It is doubtful that they would have expected to have another. In that circumstance, one might expect that the next son born would be named Joseph. He wasn’t.
Jacob is also an important ancestor. In the genealogy, he was renamed Israel, and was Joseph’s father. Thus, Jacob also bears an important lineage name, but it still might have been expected that Lehi would have used that name for a second son. A possible reason for the order of the names of the sons would be that Lehi knew he would have two sons, because they were twins. Thus, he would know that he had two sons to name after his lineage. The older was Jacob because Jacob preceded Joseph in the lineage. There is, of course, no other evidence for this hypothesis, but it provides the most parsimonious explanation for why Joseph was not the name of the first-born in the wilderness.