Once upon a time, there was this orphan, and he was raised by a kindly aunt and uncle, but it turned out that he was really a prince with a sacred duty, blah, blah, blah. Basically some farm kid turned eighteen and discovered a holy artifact by tripping over it in a field. That's not exactly destiny calling. I mean, the kid also fell face-first into a cow patty, but they don’t mention THAT in his bio.
The so-called holy artifact, which is some kind of golden mask or whatever, we don’t know, it’s hard to get near it because the kid’s being called the Chosen One or something and there’s all kinds of soldiers around him and, ick, they’ve got those darn truesilver swords and Spears of Righteous Flame and raiment of purest white and a banner that glows like the rising sun and, by all that’s unholy, do we have to listen to them singing those damn songs? The Legionnaires of Light raise their voices in joyful delight as they hack and slash at the minions of evil before them. It makes us want to retch.
The Legion of Light is a major pain in the ass and most self-respecting minions and monsters slink away from them unless there’s a Duke standing directly behind them, exhorting them to attack. The Lightketeers or whatever they call themselves were deeply disappointed that the Overlord met his demise at the hands of the Dukes, because the Legion of Light wanted badly to bring some cosmic justice to his doorstep themselves. As a result they’re spoiling for a good fight with one of the Dukes. As long as they do it far, far away, we’re okay with that.