Nephi has seen the baptism of Christ in his vision. In 1 Nephi 31:4–12, Nephi explains baptism for the remission of sins. However, after that vision we do not explicitly hear about baptism until these verses. Certainly the teaching of immersion as a means of cleansing sin continued in Nephite religion. Alma does not introduce baptism itself, but what he does is introduce baptism as an entry covenant into a new relationship with Jehovah. He was teaching those who had learned some form of the law of Moses. They understood clean and unclean. They understood sin.
What this people did not understand fully was that they could have a community separate from their city in which they might have a different understanding of God. The ability to have a divided religious community was beginning near the waters of Mormon, and baptism was expanded to become the covenant of entry as well as an act of cleansing.
The new community is defined by the way each was to care for the other. They were to bear one another’s burdens. They were to sympathize and comfort each other. Above all, of the social rules for this new division in society, they were also to be a witness for their new relationship to Jehovah. The people who remained, believing as did Noah and his court priests, had their own understanding of religion, but the new covenant of this new people was that they would stand firm in their new understanding of Jehovah as the very God who would come down to put into effect the resurrection and provide the means of repentance.