Literary: The area in which these people congregated and became a community was an area called Mormon. In this verse, Mormon (the writer) is not satisfied with a simple designation of place. He uses repetition to describe the general area. Thus it is "Mormon, yea, by the waters of Mormon, in the forest that was near the waters of Mormon." This is a literary expansion, where the initial statement is expanded by modifiers, a process we have seen in later Mexica poetry.
Once the place is set, Mormon has completed the concept of locating the people in a place. However, Mormon's interest is not geography, but spirituality. To make a transition from the more mundane conception of physical location, he repeats the triune description. In this second repetition, however, he launching from the physical into the spiritual. Rather than a location of water, trees, and land, this second triple description becomes a spiritual location. The words are the same, but they are metaphorically expanded by the phrase "how beautiful are they to the eyes of them who there came to the knowledge of their Redeemer."
We cannot know how much of the joy of the people Mormon read about, or how much he simply surmised from his own experience with coming to the knowledge of the Redeemer. Regardless of the source, he was likely quite accurate in describing the excitement of this new community.