In Ammonihah, Alma and Amulek provided the two witnesses that the law required. They do the same here. When Alma finished, Amulek stands to begin to teach. He picks up where Alma has left off. To make certain that his audience understands that he is a second witness to the doctrine of the Messiah, rather than beginning a new sermon, he reiterates some of what Alma said.
In Alma 31:8–9, Mormon noted that the Nephite religion, and therefore the understanding of the coming Messiah, had been taught to the people in Antionum. Amulek reiterates that understanding: “it is impossible that ye should be ignorant of the things which have been spoken concerning the coming of Christ, who is taught by us to be the Son of God; yea, I know that these things were taught unto you bountifully before your dissension from among us.”
Whether the people in Antionum were known as Zoramites before, or only after, their dissension from the Nephites, they had previously been taught the Nephite religion and had consciously rebelled against it. The people to whom Amulek spoke should have had that teaching. Even if they had, however, they appear to have either not understood it, or lost their understanding under the influence of the Zoramite teachings.