The prophesy. The people of Ammonihah thought that their city was so great that it could not be destroyed like Alma and Amulek told them it would. In this chapter it says that the lama ties destroyed the whole city and killed everyone in it over the course of one day. One day! A community wiped out. These were very wicked people who believed the teachings of Nehor.
Spiritual Growth. It was revealed to the people that Jesus would appear to the Nephites after he is resurrected from the dead. This shows spiritual growth because the chapters preceding this revelation, Alma felt it was necessary to establish the church again in the land because people were inactive and disobedient. He left his position in the judgement seat to do this. He spent years doing missionary work, baptizing people, organizing priests and teachers. Because of the change of heart the people experienced, they were told about Jesus being resurrected and appearing to the Nephites. They would not have known this if they had still been disobedient because they would #1 not been prepared for the information and #2 they would not have been worthy of it.