Mormon did not include all that Helaman said to his sons (see verse 13). What he did include allows Mormon’s readers to understand the desires Helaman had when he named his sons Nephi and Lehi. It also gave Mormon the opportunity to provide yet another strong testimony of the Messiah, as well as a brief recapitulation of his redemptive mission.
The imagery that Helaman used is interesting: “The devil shall send forth his mighty winds, yea, his shafts in the whirlwind, yea, when all his hail and his mighty storm shall beat upon you.” In order for the images to have any kind of impact, they must have been natural occurrences that were known, and known to be destructive. As John L. Sorenson has pointed out, those conditions, both whirlwinds and hail, are known from the Mesoamerican region where many believe the Book of Mormon took place.