I see, well I like the idea of it being a living magic kind of thing. Perhaps it is too complex for our societies to comprehend, save from the one thing.
It 'gave' us magic.
Naturally, that would create chaos, especially if the magic differs. A new struggle for control could be an outcome of it. Assuming there is a current tentative peace existing.
What if...and I am just thinking here, if there are as you said three emissaries; our third companion betrays us and steals the artifact. Thus resulting into us working together so we may stop them before they enable their entire people to wield magic or use it for more malignant purposes?

I'd go magic that is either dependant on the wielder (like Gandalf or Merlin) or on its environment (like bending the elements from Avatar).

But I'd put a price on wielding it, if not for drama's sake then for the sake of character building, as I'd like to fiddle around with it and/ or it potentially could be why our third companion betrays us.
I'm starting to bubble with all sorts of ideas here.

I'd prefer medieval-renaissance times as could potentially get your early guns in there should you want to wield those and I can have my swords and castles grin*