The story of the rebellion of the people of Morianton concludes in these verses. An army is sent that cuts off the people before they could reach the narrow pass. The presence of the narrow pass likely determined where they had to go, and therefore allowed the army to know where to meet them.
The interesting question is why Mormon included this story. It is not sufficient to say that he included it because it happened. There were many things that happened, so many that it was impossible to record all of them. Why this one?
This story allows Mormon to introduce Teancum, who will play a role later in the coming conflict, but it also allows Mormon to begin to add the threat of some unknown people in the north to the known threat of the Lamanites from the south. Mormon’s emphasis on the people in the north will increase from now to the end of his own eponymous book.