Anyway, what would cause a human to gain magical abilites? especisally as powerfull as Jason or another member of the holders of true light.
Human and elf hanky panky. As Regan notes in a later chapter, the Holders are sort of hypocritical when it comes to their attitude toward non-humans, because
any human with innate ability owes it to
elf ancestry. The trait is recessive and hard to breed for, although the Holders do try, with arranged marriages and such. However, two powerful human sorcerers might have children with weak abilities, because the actual degree of magical power seems to be governed by chance with the odds skewed toward "weak."
I.e., Jason is an aberration, not the norm.
Can we expect some Farie Creatures working with humans, or humans descandant from said Farie?
Any demons or Fey who deals with mundane humans is supposed to use a glamour to pass as human, as per various treaties and InterPlanar laws. A few species of "demon," like the Teile, have dealings (trade related) with the Holders.
Elves, and most of the non-human species avoid dealing with humans because humans are considered an immature and volatile species. The elven government refuses to deal with the Holders at all, insisting on using the Grey Brethren (vampires) as go betweens. Vampires, by virtue of their origins (Chapter One), are considered kin to the elves.
Whee! More blather than you can shake a stick at.