They're a paramilitary ultranationalist organization whose primary motivation is the eradication of all life (especially all non-elven life, but also elven and even altmer life because they believe that will return them to their primordial spirit forms from before the ehlnofey took static mortal bodies) founded in their current form as a callback to past aristocratic altmer supremacist organizations that served as shock troops, secret police, and genocidaires for the old Aldmeri Dominion. They're basically all the weird mysticism and death cult shit that runs through real Fascist ideology transplanted into a fantasy world and then handled with kid gloves because Bethesda can't commit to actually showing how evil and horrible the Elder Scrolls world is outside of like Saturday morning cartoon terms. I swear ESO does a better job of making the world weird and horrible than any mainline Bethesda game.