Gnomes are notorious for not believing in any of the common religions on Azeroth. Gelbin Mekkatorque himself, when presented with a mechagnome from Northrend, still could not be convinced to believe in the Titans.
For a long time gnomes did not practice the arts of the priest. There was simply no faith to harness the power of, but in recent years it has been discovered that it’s not faith, but willpower that fuels the spells of a priest. With that discovery, gnomes have been able to set about with a who new and different kind of holy healer, one who powers their magic with skepticism.
There is no denying that their is a life force on Azeroth. It maybe called it the light, the loa, the ancestors, Elune, but in the end, there is a very real, verifiable and repeatable way to invoke this life force to heal allies. There is also a psychic energy that can be harnessed and used to great effect to control or destroy enemies.
The fact that these two forces exist does that verify the mythologies and ‘gods’ that they are often associated with. In fact, the wide variety of beliefs undermines the chances that any are correct. If the light truly flowed from Elune, then human paladins would not be able to harness it to such efficacy.
Gnome holy priests are free thinkers, they study the theologies of all the belief systems on Azeroth. They use the teaching and mythologies as a way to focus their minds to achieve success. They don’t believe that Tir sacrifices this hand to fight against the darkness, but the imagery and the morality of the tale gives them a focus. This leads to a situation where you might hear a gnome call out to anything from the loa to the naaru when healing their allies.
Gnome discipline priests are skeptics. They have no use for the myths and legends that the holy priests use. They study the light and shadow the same way that a mage would study arcane magic. Both life force and psychic energy are naturally occurring phenomena that can be measured studied and understood. They are able to channel their magics through confidence. Their repeated testing and research have given them an understanding of how these forces are manipulated.
Gnome shadow priests are deniers and cynics. They may not know exactly how their magic works, but that doesn’t matter as much as the fact that they know YOU are WRONG. These gnomes use psychic energy to project their doubts and disbelief in to the minds of a target. Once afflicted, the subject loses their own faith and their mind either submits to the will of the gnome, or is torn by the thought that everything they know and love is a lie.
Gnomes have no cultural concept of the divine. They may not see value in the idea of worship, but these gnostics still possess the convictions and the strength of will to harness the powers of light and dark.