During this time, King Mosiah, the son of Benjamin, was the king in Zarahemla, and kings in this system saw themselves as the father of their people. Mosiah had been justifiably worried about those who had left Zarahemla and gone elsewhere, so he allowed Ammon and three other men to go to the land of Nephi, looking for his children. This accounts for the great joy Mosiah must have felt to learn of the success of Ammon’s mission.
This might be compared of the premortal life, in which the people have left the presence of the heavenly king and have gone somewhere else. Now, as the people return to Zarahemla, we can see this as a type of repenting and returning. There was great joy, as there will always be divinely royal joy in heaven when we finally make it back.