Magic, in Chronicles of the Psi, comes from the Gods, or comes from mutations. Thus the two magic-wielders in the chronicles are Priests and Sorcerors. Magic is then broken up into three categories:
The reason for the existance of magic is debatable. It's not clear whether the Gods create magic, or if they shape it to do their bidding. The fact that the Outer Plane is made of Magic, and the Gods merely inhabit it, would seem to indicate that things are a little more complicated than they may seem.