Editorial: Mormon returns to condensed narrative from the embedded discourse. In the next verse he describes the official bestowal of authority on Mosiah, but in this last discourse simply gives Benjamin's instructions on the nature of the coming meeting. Why did Mormon select that passage for citation, and condense the more ceremonial transfer of symbols? The answer must lie in the importance of the new covenant. Until this point in time, there were people of Mosiah and people of Zarahemla. Mormon is highlighting the unification of those two remnants of Israel into a new single people, represented under a refreshed covenant that carried over from the previous peoples.
Political: The transition from verse 16 to 17 is critical to understanding the nature of verse 17. When Benjamin gives Mosiah "charge concerning the affairs of the kingdom," we are seeing the transferal of power from Benjamin to Mosiah. Along with the important affairs, the political realities and exigencies, Benjamin delivers some specific items: "the records which were engraven on the plates of brass; and also the plates of Nephi; and also, the sword of Laban, and the ball or director."
These are all ties to Jerusalem. They are physical proofs of the preservation of the people by God. As historical relics they would be one thing. They are not simply historical, however, but embued with highly charged religious meaning. For Benjamin, it is the religious meaning that is most important, witnessed by the definition he gives of the director. Benjamin highlights the religious meaning of the director, not the historical one. In the combined world of religious politics, these sacred relics serve as the physical reminders of the sacred covenant between the people and God. They are the physical witnesses of God's fulfillment of that promise.
The essence of these relics lies in Benjamin's discussion of the Liahona, a director that shows the way, but only upon conditions of righteousness. A righteousness that is the condition of the covenantal promise Benjamin makes.