I think that the Empyream should be all about "My way is the only right way" and "The ends do justify the means".
Think Spanish Inquisition (not the Monty Python Version) or the "Wheel of Time"s Children of the Light.
That's how I've always pictured the Order.
There's not much source material about the Empyrean, but I imagined them as Buddhist.
Their Civilopedia entry:
Where the Order values law, the Empyrean values wisdom. Adjudication started from the teachings of Lugus and punishment is not based on adherence to a labyrinthian codex of laws, but from direct consol on the merits of each case. Social equality and impartiality are the model between a government and its citizens as well as between empires. As such the Empyrean gives equal voice to small empires as it does those that dominate Erebus.
seems compatible with the Buddhist ideal:
the perfect peace of the mind that is free from craving, anger and other afflictive states
The Empyrean leaders could only pursue social equality and impartiality if they were free from personal motives like anger and greed. I like to imagine the Empyrean leaders meditating on enlightenment (which, in the FfH universe, would probably mean an understanding of the will of the One).
Of course, like any powerful religion, some people will display the outward symbols of the religion without believing its teachings.