This verse tells a very terse tale, and one that is perhaps hard to imagine. An armed force is met by a body of unarmed people. They fall upon them and begin killing them. Why is it that they would commit such a wanton slaughter? First, we must remember that the function of warfare was different for Mesoamericans. The process of combat was just as important as the outcome. Thus the combat itself was emphasized, and the capture of prisoners an important outcome. When faced with unarmed opponents, actions that might have been designed to wound and capture against an armed opponent would easily have been deadly.
Secondly, it is quite likely that the Lamanite army worked themselves into an excited state, and that the adrenaline rush of the battle would have begun the slaughter before the conditions completely registered. Indeed, this is what the text appears to tell us, that there were those who began the slaughter, an then came to an understanding that this was a very different sort of combat – a type in which there was no honor to be had. It was then that those assailants ceased their attack.
Variant: The Original manuscript, Printer’s manuscript, and the 1830 edition all begin verse 21 with “And it came to pass that when…” (Book of Mormon Critical Text. FARMS, 1967, p. 667).