Alma 43

As the Lamanites departed out of the land of Antionum into the wilderness with a secret plan to attach the land of Manti -

"...Moroni, also, knowing of the prophecies of Alma, sent certain men unto him, desiring him that he should inquire of the Lord whither the armies of the Nephites should go to defend themselves against the Lamanites.
24 And it came to pass that the word of the Lord came unto Alma, and Alma informed the messengers of Moroni, that the armies of the Lamanites were marching round about in the wilderness, that they might come over into the land of Manti, that they might commence an attack upon the weaker part of the people.  And those messengers went and delivered the message unto Moroni.
25 Now Moroni, leaving a part of his army in the land of Jershon, lest by any means a part of the Lamanites should come into that land and take possession of the city, took the remaining part of his army and marched over into the land of Manti."  (Book of Mormon | Alma 43:23 - 25)

In my mind, this demonstrates the great faith and obedience that Moroni possessed in God, revelation, and his priesthood leaders.  Any error could be devastating.  Can you imagine this happening today.