Crystals used to hold the souls of the Heroes of old. The original kingdom of Kel Teara used them so that there greatest heroes would never pass but instead passed on.
This is the major reason for the fracturing. The gods did not like being cheated the souls of there servants who they have invested so much. On death the soul was theirs and they would not be denied. The Kel Tearans seeing there doom sided with what they call The One God.
The battle between The One God and the group of gods lead by Pelor are what caused the lands to split and fracture and nearly whipped out all life on the planet.
It is later learned that someone who accepts the crystal doesn’t just get the heroes of the past memories and power but eventually it takes them over and erases who they where. The process requires someones body that has some power to survive the transition.