The ordinance of baptism is not explicitly an important aspect of Nephite religion until Alma1. By the time of Alma2, the ordinance has become so definitive that the Messiah enters mortality at least partially to be baptized. What this means in terms of Book of Mormon doctrine is that the ordinance of baptism has completely supplanted the Jewish rite of animal sacrifice for atonement. Alma’s address is a milestone in showing the movement away from the sacrificial cult of Israel and toward a more spiritualized worship that is reminiscent of Christianity and even of Israel after the destruction of the Jerusalem temple by the Romans. It seems probable that separation from both the physical temple in Jerusalem and from the Levite priestly lineage led to responses that were similar among both the Old World Christians and the pre-Christian Nephites in the New World. Both instances shifted religion from the communal to the individual.
For example, Alma states unequivocally that the Atoning Messiah is coming to “redeem those who will be baptized unto repentance.” There is absolutely no indication of any other required sacrifice. The religion has been transformed into a spiritual relationship with Yahweh rather than a communal relationship maintained by animal sacrifice.