This verse contains the fascinating statement that the Gentiles “shall be numbered among the seed of thy father.” This is a statement made to Nephi. Therefore, the most logical referent for “thy father” is Lehi, suggesting that the Gentiles will be redeemed by being included in the house of Lehi. Of course Lehi is also of the house of Israel, so the blessings attached to Abraham may pass through to the adopted Gentiles, but Nephi is being told that it will happen through some connection to Lehi.
McConkie and Millet explain this phrase: “Most of those designated as Gentiles in the Book of Mormon are, indeed, members of the house of Israel by lineal descent. Many of them, however, have not entered into the covenant, for they have not taken upon them the name of the Mediator of that covenant and entered into the covenant gospel through an authorized baptism in his name.” McConkie and Millet are certainly correct about the Gentiles’ inclusion in the benefits of Israel, but they do not deal specifically with adoption into Lehi’s line. Reynolds and Sjodahl note that this adoption will come through Lehi but have no other comment about why this particular line is appropriate. Neither Nyman nor Ricks comment on the adoption through Lehi, although both note the adoption of the Gentiles into Israel.
I cannot answer the question of why that lineage is required or how it will work. However, I can suggest that this promise should awaken us to the fact that this is a revelation being given to Nephi, not to us. While we have a part in it, most of the meaning is directed to Nephi’s perceptions and understandings. Nephi’s concern was with his father’s posterity in this new land. The promise that salvation would come through his father’s line would have been a tremendous consolation for the vision of apostasy and destruction that was also part of his vision of the future. For Nephi, this salvation through Lehi would mean that some portion of Lehi’s descendants would be instrumental in saving the much larger number of Gentiles in the land. (See commentary accompanying Mormon 5:12 for Mormon’s similar interest in the people of Israel.) Perhaps this promise is tied to the delivery of the record that his descendants will keep and which Nephi will begin—the Book of Mormon.
The first promise to the Gentiles is that they will be redeemed as they accept the newly revealed truth, the restoration of those lost “plain and precious parts” of the gospel. They will be numbered with Israel and receive blessings promised to Israel.
The second promise to the Gentiles is their preservation from captivity. This may mean that freedom from captivity is attached to a location and perhaps a government. While this description might apply to the United States and Canada, it excludes much of the world’s population from these benefits. An alternative reading is that the captivity is not to other human beings but to the great and abominable church—a spiritual captivity from which anyone who accepts the gospel will be free, regardless of locale or government. This reading fits better with vision of the great and abominable church, which is about to resume than with the gospel’s impact on the modern world. It is supported by the increasing specificity of the next two verses.
Variant: The printer’s manuscript and 1830 edition both read: “harden not their hearts against the Lamb [and if it so be that they harden not their hearts against the Lamb of God.… ]” Beginning with the 1837 edition, the second occurrence was removed, obviously to simplify the reading. An argument might be made that the printer’s manuscript applied literary emphasis, but the 1837 deletion preserves the essential meaning.