Redaction: The structure of this inserted quotation allows Alma to record not only the events of the discourse, but his reaction. Because he is both recorder and protagonist, his viewpoint is emphasized.
Verses 2 and 3 are a paired set, with verse 2 being the contending statement and verse 3 being Alma’s inserted commentary on the argument. Verses 4 and 5 form a similar set of point and counterpoint, even though Alma’s insertions interrupt the logical flow of the Ammonihahite contention.
The counterpoints between the Ammonihahite contentions and Alma’s responses tell us not only about the Nephite gospel, which is Mormon’s intent, but also about the order of the Nehors. These arguments, in one form or another, have plagued and will continue to plague true believers throughout the Book of Mormon. (See “Excursus: Religion of the Nehors,” following Alma 1.) We began to see the outlines of this competing religion in the confrontation between Abinadi and the priests of Noah (significantly including Alma1). This contention between the Ammonihahites and Alma continues to enhance our understanding of this competing religion that was so significant it was considered a threat to the peace of the Nephites.
Alma’s comments about the end of the world may suggest that the Nehorites reject prophecies of apocalyptic destruction at the end of time. Such a belief might be a logical result of denying the Messiah, though they most customarily deny the Atoning Messiah, not necessarily the Triumphant Messiah. However, the Nehorites might conflate the two when viewing the Nephite position. Mormon takes pains to make the two parallel. Or perhaps the Nehorites are rejecting an immediate apocalypse accompanying the birth of the Messiah as preached by the Nephites, or even an apocalypse associated with the Messiah’s predicted appearance in the New World.
Rhetoric: The first argument presented by the Ammonihahites is one of authority. While modern LDS readers assume Alma’s authority, the Ammonihahites did not. Their first question to him is “Who art thou?” They were not asking for his name and title but challenging his essential right to preach. Their claim that they would not believe a single man if he were to tell them that the world were ending is clearly meant to be sarcastic, from Alma’s inserted comment. He notes that they did not understand that this truly would happen.
We lack enough context to tell us why we have these two particular pieces of the exchange, but it seems reasonable that Alma had already been following the angel’s instructions—that is, prophesying the destruction of Ammonihah if the inhabitants did not repent. Certainly they would not believe Alma’s message, since they had no faith in the messenger.