The people understood that Moroni was calling them to arms. They came “with their armor girded about their loins.” The next description is another physical representation of a covenant. In the comments on Alma 44:14, the idea of a simile curse was discussed. The curse was that should the Lamanites not accept the covenant of peace, they would fall to earth just as Zerahemnah’s scalp had fallen.
This is not a curse, but a simile covenant. The covenant was made, and the simile invoked the nature of the penalty should they break their covenant. They made it clear that they intended to keep the covenant to fight for their religious liberty.