Prophecies and Promises
There are a handful of prophecies and promises found in this chapter. I only note them to bring to attention the fact that the prophecies and promises Alma spoke indeed were fulfilled.
In Alma 9:12, he warns the people of Ammonihah to repent or be utterly destroyed from off the face of the earth. He then explains that the Lamanites are better off than them because the Lamanites have not sinned against greater light and knowledge. (Alma 9:21-23) In Alma 9:18, Alma specifically tells them that if they do not repent, the Lamanites will completely destroy them. Because the people of Ammonihah did not repent, the prophecy was fulfilled. (Alma 16:9-10)
Alma also prophesies that "at some period of time they [the Lamanites] will be brought to believe in his word, and to know of the incorrectness of the traditions of their fathers; and many of them will be saved, for the Lord will be merciful unto all who call on his name." (Alma 9:17) Roughly at this same time, the sons of Mosiah were diligently working among the Lamanites and many of the Lamanites were converted and saved, thus fulfilling this prophecy.
Lastly, Alma repeats the oft spoken promise of the Book of Mormon. In Alma 9:13 he reminds the people that if the keep the commandments they will prosper in the land. If the do not keep the commandments, they will be cut off from the presence of the Lord. There are numerous examples in the Book of Mormon of this promise being fulfilled.
Tradition of your fathers
The reason the Lamanites are in the state that they are in is because "of the incorrectness of the traditions of their fathers." (Alma 9:17) Because Laman and Lemuel did not follow in the tradition of their father, they were cursed and thus brought the same curse on their children.
Alma warns the Nephites in Ammonihah that they have "forgotten the tradition of their fathers." (Alma 9:8) Because the Nephites have forgotten the tradition of their fathers of keeping the commandments, they will be destroyed too, if they do not repent.
Are there traditions in our lives that we need to keep in order for us to spiritually survive? Likewise, are there traditions in our lives that are not in harmony with the Gospel? The Nephites were blessed because they kept the righteous traditions of Lehi and Nephi. The Lamanites were cursed because they did not keep the righteous traditions of Lehi, but followed in the unrighteous traditions of Laman and Lemuel. We would do well to remember to maintain righteous traditions while ending unrighteous traditions in our own families.
I remember Elder Scott delivering a powerful talk on ethnic traditions and how some of those conflict with the teachings of the Gospel. He offered this counsel in overcoming those conflicting traditions, "You may ask how can one determine when a tradition is in conflict with the teachings of the Lord and should be abandoned? That is not easily done. I have found how difficult it is as I work to overcome some of my own incorrect traditions. Yet recognizing the need to do it is a major step towards success. Customs and traditions become an inherent part of us. They are not easy to evaluate objectively. Carefully study the scriptures and counsel of the prophets to understand how the Lord wants you to live. Then evaluate each part of your life and make any adjustments needed. Seek help from another you respect who has been able to set aside some deeply held convictions or traditions that are not in harmony with the Lord’s plan. When in doubt, ask yourself, 'Is this what the Savior would want me to do?'" (Richard G. Scott, “Removing Barriers to Happiness,” Ensign, May 1998, 85)