http://www.wowpedia.org/Light
"No one feels he deserves it... its grace, pure and simple... but the Light loves us anyway. - Uther the Lightbringer"
"While most followers of the Holy Light do not worship any gods, the power apparently does come from some sapient being, or beings, or force, known simply as the "Light" for lack of a better description.[citation needed] One source of the Light (though not the only one) is the race of beings known as the Naaru. During the draenei's exodus from Argus, Velen and his followers were imbued with Light-given knowledge and powers by this (otherwise unknown) race of incorporeal beings."
"The young High General Abbendis seems to believe that the Light is some kind of sapient entity with a will, which it expresses in ways that that are not meant to be understood. She writes that it calls to her in the [The Path of Redemption] and [The Diary of High General Abbendis], saying "Come to me...". She believes that it is able to take notice of believers' good deeds, works and prayers. She states that the force of its voice has clarity and sense of purpose. However, the entity that calls her may be something else far more sinister, as she discusses in her diary that it commands her to abandon the Scarlet Crusade to its doom, an act she believes is dishonorable."
I honestly wouldn't rule it out. There's hints that Elune may be a naaru(or some other deity) , same with the Earthmother/Sunwalkers.
I dunno, I myself is more of a 'seeing is believing' person. While faith is the fueling source for the Light, I personally think there needs to be something bigger or larger is rewarding that faith with power. Otherwise, literally any human could wield the Light as a natural talent if their faith held true, similar to how the Draenei with the Gift of the Naaru. (Perhaps the human spirit is it, as Sol suggested.)
Don't know, I've always though the naaru were the source of Light and the humans were believing in tenets that matches the naaru's mindset so they rewarded them.
However... I've found interesting stuff.
"The Holy Light teaches that there is a connection between the self and the universe. This connection manifests as what we feel through both senses and emotions. When a person is moved, through seeing something breathtaking or feeling love for another, that emotion connects him to the universe. Experiencing the emotion ensures that he exists, as something within him felt the emotions or processed the sensual awareness. Because he exists, so must the universe that gave him that feeling. From there, he can act upon the universe, causing more changes to create feeling in others. Thus, the followers of Holy Light seek to make the world a better place by being true to their own emotions."
(Am I the only one that sees this as an opening for paladins to sleep around and love freely to make other people happy?)
"Some Knights of the Silver Hand apparently believed that, "...after death, a mage's soul would be condemned to the same pit of darkness shared by the mythical demons of old. This no matter how pure their soul might have been otherwise."[2] Essentially, damnation.[3] Members of the church would sing the hymn Deo Gratias, "Thanks be to God". A leading paladin, Duncan Senturus, believed that tasks and paths were often chosen by a "higher power".[4] He believed that evil things were ungodly and devilish."
(Totally an opening for Dragon Age Templars-like paladins.)
The more I know!