The function of these verses is to indicate that the ball, or director, accomplished its purpose. The family departs into the wilderness as directed. They were following Jehovah’s will, therefore the director showed them where to go.
This story introduces the traveling family, and the need to hunt for food. The fact that they take their bows and arrows to provide food becomes critical as the next part of the story develops, and the bows are no longer available.
This part of the story is simply told because its basic function is to move to the next important story. Nephi’s stories have been increasingly showing his growing importance to the family, and the story of the broken bow is a continuation of that trajectory.