The book of Omni opens much as the book of Jarom did. Jarom 1:1 noted that his father had commanded him to keep the genealogy. Omni 1:1 notes that his father commanded him to preserve the genealogy. As with the comments on Jarom 1:1, it is probable that the term genealogy used in this sense is the father-to-son transmission of the plates and the responsibility to write on them.
The small plates had a very specific command associated with them when Nephi first created them. They were for “the special purpose that there should be an account engraven of the ministry of my people” (1 Nephi 9:3). The large plates contained the “account of the reign of the kings, and the wars and contentions” (1 Nephi 9:4). These commandments, concerning the content of the two plate traditions that Nephi created, continued through the existence of both of those traditions. The large plates continued to record the deeds of the kings, or later, chief judges, until Mormon himself wrote on the large plates. The small plates were clearly transmitted with the command that they preserve things of the ministry.
For that reason, Omni notes that he has “fought much with the sword,” and that he had not “kept the statues and the commandments of the Lord” as he ought. Therefore, he did not believe that he had anything to add. The wars or battles in which he had participated would have been recorded on the large plates. Apparently, his life was spent in things that were more suited to the other plates, and not the special command for the small plates. Nevertheless, he keeps his father’s command that he should preserve the lineage record. He writes a little, and then passes the record to his son, Amaron.