Moroni’s first tactic was to issue a challenge to a fair fight in the open. It is no surprise that the Lamanite captain, Jacob, refuses. Even if he were confident of victory, there would have been little advantage to him. His army was in an excellent and sustainable position; he posed a very real danger to the Nephites while they posed relatively little to him. He had no incentive to accept.
Yet obviously Moroni had a reasonable expectation that Jacob might accept the proposal. Sending a representative to the city before a proposed attack was a traditional part of Mesoamerican warfare; the later Aztecs, for instance, typically sent ambassadors to target cities offering them the option of surrender to the Aztec hegemony. The other option was, of course, military action.