Mormon is deliberately humanizing his story by attributing dialogue to the messengers. The literary effect is to involve the reader more fully in this dramatic action, therefore underscoring Nephi’s prophetic qualities and meeting his larger purpose as a moral historian.
Culture: Although there is no way to confirm it, I hypothesize that sending five men may have harmonized with the Mesoamerican significance of five directions, one for each of the cardinal directions, and another for the center. Sending five could therefore indicate a “complete” witness or, symbolically, the witness of the “whole world.”