These verses are an essential element of the story, as Mormon needs to explain the transition from prostrate servants to a dead king. The first important point is that the king allowed the servants to rise. Thus the servant who was to stab the king is performing a normal and expected action when he rises. Of course he must rise to be in a position to strike at a vital part of the king’s body. The second point is that the king’s arms were raised. It is possible that this action also placed the king in greater physical jeopardy. With his arms raised he was less able to use those arms to fend off the surprise attack, and the arms were not in a position to be in the way of the blade.