Nephi’s vision has been leading to this point. Nephi understood, even before this vision, that Lehi’s family would become a separated people from the main house of Israel. The vision is the picture of how that separation would be healed. It wouldn’t be a simple process, and would involve events on two different hemispheres. However, it would come together.
Nephi has seen that there would be two records, and has seen that the Gentiles would ultimately inherit both the land and the promise that is attached to it. After showing how the two records would join, with the New World record filling in plain and precious things lost from the Old World record, Nephi’s visions turn to the Gentiles themselves.
The definition of a Gentile is that he or she is not an Israelite, not part of the covenant people. There is no complete unification until the house of Israel is unified. This comes when the Gentiles “shall hearken unto the Lamb of God.” When that happens, the Gentiles “shall be numbered among the house of Israel.
Isaiah had promised a gathering of scattered Israel. Nephi’s vision not only sees Lehi’s seed as scattered Israel, but Israel itself as partially lost. The Gentiles will inherit the Gospel through the Old World book, and both the New World Israel and the Gentiles as newly Israel will be gathered into the House of Israel.