Anthropological: These verses provide some tremendously important information, but they do so in such as way as to be so 'matter-of-fact' that it is easy to miss the significance of the statements. A quick and superficial reading of the verses tells us that Benjamin was a good father in that he taught his children, and particularly taught them the gospel. While true enough, such a reading misses the real import of the text.
First, we note that Mormon indicates that Benjamin's sons are being taught the words of two different record traditions. The second is actually named, and its naming serves to identify the first by elimination. Verse 3 tells us very specifically that the sons are taught from the brass plates. Since this named record tradition follows the teaching about the words of the fathers in verse 2, by default we may assume that they are also taught from the large plate tradition. Since "the prophecies which had been spoken by the mouths of their fathers, which were delivered them by the hand of the Lord" are specifically not those on the brass plates, and are specifically "delivered by the hand of the Lord," we may infer that the Mormon means that they were taught in the traditions of the prophets who were contained on the plates of Nephi. The plates of Nephi are part of the set of items transmitted upon the bestowal of kingship, as we will see later, so they are quite literally "delivered." The phrase "by the hand of the Lord" would be the recognition that the preservation of the plates was under the care of the Lord, a condition most recently demonstrable with the exodus of Mosiah 1 from Nephi.
Second, it is important that Mormon mentions that"...he caused that they should be taught in all the language of his fathers." We have noted previously that the word "language" in the Book of Mormon has ambiguous connotations, at times possibly covering both language proper and the larger category of culture. In this case, however, it may be most appropriately language proper, for we are told that part of the reason that they were taught was " that thereby they might become men of understanding; and that they might know concerning the prophecies which had been spoken by the mouths of their fathers,"
The cultural meaning might still explain "men of understanding," but the he final phrase ties the teaching of "language" to the words of the large plates. They learn the language specifically to be able to "know concerning the prophecies which had been spoken by the mouths of their fathers." We may therefore assume that by "language" the minimum possible interpretation is that they were taught to read. Certainly a literate person would qualify as one of the "men of understanding" and also allow them to read the "prophecies which had been spoken by the mouths of their fathers." While this minimal reading is certainly accurate as far as it goes, I suggest that the teaching of the language of the fathers was more literal, and included a language as well as a capacity to read it. This will become most clear in the next verse.
At this point, however, it is sufficient to note that the teaching of language was thought to be of such unusual significance that it was mentioned even in Mormon's abridgement. What is never of sufficient importance to mention is that a child learns the spoken language of the parents. That is expected. What is unusual, however is the teaching of a second language, hence the need to mention this special learning for the sons of Mosiah. Precisely what they were learning comes from verse 4.
Editorial: Verses 1 and 2 are wholly Mormon's words. They are based remotely upon the data on his source plates, but these verses are a summary statement recounting what was surely detailed data on the plates of Nephi into the shortest of summaries. This editorializing continues until the middle of verse 3 where we have a citation of a discourse of Benjamin to his sons.
Mormon has selected this discourse because it shows one of the ancient ones describing the value of the information on the plates. Mormon would be very sensitive to such value as his task in creating an abridgement was to preserve that value for future generations. He therefore saw this discourse as directly relevant to the purposes he had in creating his plates, and included the citation from the source material.
Mormon's textual set up for this citation is the quick recounting of the necessary historical background against which the discourse makes sense, but the purpose is to preserve the discourse, not recount history. That we may extract historical/anthropological data from his introduction is felicitous, but is an artifact of commonplace information to Mormon, not data that he was consciously attempting to communicate. Indeed, virtually all of Mormon' choices will be governed by spiritual rather than historical criteria (using those concepts in their modern sense).