Doctrine and Covenants 101:
53 Ought ye not to have done even as I commanded you, and—after ye had planted the vineyard, and built the hedge round about, and set watchmen upon the walls thereof—built the tower also, and set a watchman upon the tower, and watched for my vineyard, and not have fallen asleep, lest the enemy should come upon you?
54 And behold, the watchman upon the tower would have seen the enemy while he was yet afar off; and then ye could have made ready and kept the enemy from breaking down the hedge thereof, and saved my vineyard from the hands of the destroyer.