It appears that Jacob is quoting Isaiah but in a context that makes the promise intelligible in an oral setting. Because the first person of the original text would have no antecedent and might therefore be confusing, Jacob reshapes the quotation slightly for clarity but does not alter the essential meaning. Another possible explanation is that Jacob knew his people were sufficiently familiar with the quotations to recognize them, even with a slight variation, and understand them without further explanation.
Joseph Smith apparently preferred Jacob’s more explicit definition of the speaker in this verse, for his rendition of the passage in the Joseph Smith Translation is closer to Jacob than to Nephi or to the King James Version: “But thus saith the Lord; even the captives of the mighty shall be taken away, and the prey of the terrible shall be delivered; for the mighty God shall deliver his covenant people. For thus saith the Lord, I will contend with them that contend with thee, and I will save thy children” (JST, Isa. 49:25).
Text: The 1830 edition has no chapter break here.