Alma 13:21-26. Alma Didn’t Know When Christ Would Come
Why did Alma not know when Christ was coming (Alma 13:21-26) even though he possessed plates and Lehi and Nephi had written precisely when he would arrive, i.e., 600 years from the time Lehi left Jerusalem (1 Nephi 10:4; 19:8; 2 Nephi 25:19)?
We do not know if Alma had read the small plates on which the 600-year prophecy was written, and we do not know if the large plates mentioned that prophecy. Mormon, who had access to all the Nephite records, only discovered the small plates part-way through his preparation of the Book of Mormon and decided to add them to his own (Words of Mormon 1:3-4).