As a refresher, “all these things” that the sons of Mosiah have been doing were attempts to rectify the effects of their preaching against the church in the land of Zarahemla.
Because of their clearly privileged position as the sons of the king, they had most probably been very instrumental in diverting many away from the church in Zarahemla. It was therefore to those people that they had most directly hurt by their actions that they made their first “mission.”
What we have in this next section is a secondary “mission.” Once the sons of Mosiah (and “a small number with them”) and spend some time in the land of Zarahemla, they had apparently done what they could to correct the effects of their earlier error. What they want to do now is continue to preach the word. They ask to mount a mission to the Lamanites. Why the Lamanites?
In the traditional sense of Book of Mormon interpretation, the Lamanites would have been the only other people around, and if all of Zarahemla were converted, there would be nowhere else to go. Even interpreting “Lamanite” as a term for all non-Nephites as we have done in this commentary, it might still be considered logical to turn to the Lamanites if all of Zarahemla were converted.
It is possible that there is more than this behind the request to preach to the Lamanites. Given the nature of the apostasy of the sons of Mosiah and Alma the Younger, it is very likely that they had been converted to the Lamanite religion (at least the type of Lamanite religion that was practiced by Noah and his priests). Assuming that this were true, it would be a very natural thing for the thoughts of the sons of Mosiah to turn to those people who were so recently admired that their religion and philosophy had been adopted by the sons of Mosiah. This becomes even more likely when we remember the number of times that the Lamanites have been described pejoratively by Nephites (such as 2 Nephi 5:21-24, Enos 1: 20, Mosiah 9:12, and Mosiah 10:12). With this apparent cultural preconditioning against anything Lamanite, we might expect that the sons of Mosiah might never consider preaching to them.
Just as did Zeniff (Mosiah 9:1), it would appear that the sons of Mosiah found much that was good in the Lamanites. They appear to have adopted some of it, and now naturally turn to those people to give them the joy they have so recently found.