Mosiah takes the question to the Lord, and the Lord sends the sons of Mosiah on their mission. It will be an important, and a successful, mission. After Mormon introduces the reason that the sons of Mosiah will not be in the land of Zarahemla, he simply notes that he will tell their story later. The point of telling this much of their story is to set up the story of the change to the political organization in the land of Zarahemla.