Nephi spends much of a chapter on the important event of returning to Jerusalem for the plates of brass. It is certain that some version of that account was on the record that Mormon created to describe the Nephite origin story. This verse presupposes the value, not only the current value, but the blessing of the possession of this set of plates. Benjamin is echoing the reason that the Lord commanded Lehi’s sons to return for them, an echo that would not have been easily understood without having already been written in Mormon’s abridgment.
Most interesting is that he brings up teaching and language again. This time, Benjamin says of Lehi: “he having been taught in the language of the Egyptians therefore he could read these engravings.” This suggests that the plates of brass, a record kept in Egypt, was written in Egyptian, and the ability to read Egyptian was required to read the plates of brass. This, therefore, suggests that when Benjamin’s sons are taught “all the language of [their] fathers” (in verse 2), it specifically referred to learning to read the Egyptian text on the plates of brass.