The Light is a cosmic force, much like the Void. Naaru are a product of the Light, much like Titans are (to a lesser extent). As such, the Light has no will, is just power that can be called upon, in the Light's case through faith and willpower. That's why the Light answered the call of the deranged Scarlet Crusade or the even more demented Vindicators of the Twilight's Hammer.