The logical result of true repentance and understanding of the Savior’s mission is to desire baptism. Therefore, Alma calls the people to be baptized. The teaching itself raises no questions, but teaching it to this particular people does.
This is the people who desired of Ammon that they be baptized, for they had heard of Alma the elder baptizing. Although Ammon did not feel he could perform that ordinance for them, they were later baptized (see Mosiah 25:17–18). Why then does Alma the younger ask them to be baptized?
The ultimate answer is that the text doesn’t give us enough information to know. There are two possibilities:
1. There were those among them who had not been baptized. It is not known whether they were people who had later joined the former people of Limhi, or whether some of the children of the people of Limhi were too young to have been baptized.
2. The Nephite baptism retained some of the aspects of the mikveh in the law of Moses. That was a ritual cleansing by immersion that would happen more than once. Thus, there was a baptism as a symbol of entering the church, but perhaps a repeated baptism that symbolized a renewal of cleansing and perhaps a renewal of covenants. In earlier days of the Latter-day Saint church, members who had already been baptized might be baptized again as an act of renewal and recommitment to their covenants.