Although it is possible that there was something in the untold history of Ammonihah that fits the events that Alma discusses, it seems more probable that things like conversing with angels and having been spoken to by the voice of the Lord refer to prophets of the Nephite religious tradition. Nevertheless, Alma presents the Nephite tradition as the Ammonihahite tradition. In particular, Alma appears to invoke the long Nephite history under the monarchy, and Mosiah in particular, when he notes that the Nephites have had the gift of translation. Mosiah translated the plates of Ether, an event that would have been within the lifetime of many in the city of Ammonihah.
Alma reprises Jehovah’s power to save by mentioning Jerusalem again. The point of all of these advantages of living according to the covenants that Jehovah made with the Nephite people is to contrast the current position of the people of Ammonihah. As a people who have received all of these benefits, it is a greater sin to leave them behind than it is for the Lamanites, who had never had those advantages. This verse parallels verse 16 where Alma also indicated that it would be better for the Lamanites than the people of Ammonihah at the last day.