The oldest traditions of the Nephite people were that they had come from Jerusalem. The first Nephi had written that they were to be considered the parts of Israel that were on the isles of the Sea. Of course the passage of time had refocused the Nephites on this land rather than the one they had left, but the presence of the Atoning Messiah in their midst who clearly had recent connections to Israel of the Old World would have inevitably raised questions in the minds of many as to whether or not the time of their reconciliation and reunification was at hand.
What Jesus does now is prepare the apostles with the information that they need for that answer. How do the Nephites related to their distant (in space and time) brothers in Israel? Jesus begins by not only noting the difference, but confirming that difference as a divinely appointed one. In verse 13 Jesus reminds the twelve that this is the land of inheritance for the descendants of Lehi. This would be a clear statement that there was no imminent reunification of Israel. That function was to remain for the role of the Triumphant Messiah.
Not only is this land their inheritance, but it will remain a separate one for some time longer. Jesus declares that he was commanded of the Father not to tell those in Jerusalem about it. Therefore, the Nephites cannot expect that Israel will be coming to them any time soon. Those who are scattered are to remain scattered for the time being, and this includes others who are not the Nephites.