All races create great edifices in praise of their gods, from the crude idols of Gork and Mork built from the dung of greenskins, to the magically flaming shrines the High Elves build in their worship of Asuryan. To defend or despoil these important symbols is a strong incentive for any army to fight a battle.
An ancient idol allows the controlling army to re-roll failed Leadership tests to rally fleeing units.