Culture: Here is the most explicit correlation between Alma’s baptism and the entry by covenant into a subset of society—a church. Limhi’s people have been with Ammon for some length of time, perhaps a year. They have repented of Noah’s apostate ways and returned to a belief in Yahweh as understood and taught by Ammon. Thus, Alma is not baptizing unbelievers, but believers.
While it is tempting to suppose that this baptism is required to return the Limhites to the Nephite religion, clearly Ammon refused to baptize (Mosiah 21:33). This ordinance waited for Alma, just as those who left Lehi-Nephi to go with Alma were baptized in the waters of Mormon.
The mention that those baptized “did belong to the church of God” underscores the concept of a church. For the first time, Nephite society shows an explicit demarcation between a religious congregation and those who were still part of the community but not part of the church.