Textual: This is the sermon of Alma the Younger to the church in Zarahemla (see verses 1 and 2). Thus this is a sermon to those people who should know Alma as well as anyone, as this is where Alma has lived and served as both the chief judge and the leader of all of the churches. It is therefore interesting that Alma begins by establishing his authority to speak through the authority of his father. He has a reason for doing this that is much beyond simply establishing his own authority to speak, and authority that would have been unlikely to have been in question.
Alma refers to his father because his father faced the same kind of opposition in the land of Nephi that Alma the Younger is facing in Zarahemla. Alma is attempting to purge the present by reminding his people of the past. The current social contention is similar to that which Noah and his wicked priests had promulgated, and Alma will plead his case that their current situation may have a similar fortunate end, if this people will follow the example of their fathers of faith in God.
To this end he begins by returning the audience to the important part of the story of his father, the establishment of the church near the Waters of Mormon. Thus the current church is to conceptually connect themselves with that earlier church.