Lehi pursues the Lamanites to keep them moving in the desired direction—straight into Moroni’s army. Probably, Moroni had sent a courier to Lehi to let him know the status of this maneuver. Couriers may move through occupied territory where larger units could not. Lehi (with Teancum’s added force) moves cautiously, fast enough to keep pressure on the Lamanites but not so fast as to catch them before Moroni would be in position to attack as well.