Alma has given a review of a story in the scriptures, and not refers the people to those texts. This tells us both that the story of Melchizedek as Alma retells it was in the Nephite scriptures, and it clearly tells us that the Ammonihahites had a copy of the Nephite scriptures. The order of the Nehors did not deny the scriptures, they simply interpreted them very differently. Alma warns the people lest they also interpret this story differently. If they do not understand the scriptures just as Alma has explained them, they will literally be destroyed.
Modern Application: The Ammonihahite problem if interpreting texts is certainly not surprising, and is hardly uncommon in the modern world. There are large numbers of people professing to be Christian who share the same scriptures, yet base very different beliefs on those same scriptures. Alma gave the correct interpretation to Ammonihah, and we may expect that the same model of a prophet providing the meaning to the text will continue today. While the destruction promised the Ammonihahites was real and proximate, it still holds as a spiritual consequence should we attempt the same wresting as the Ammonihahites had been doing.