God Magics & Clerical Mechanics
The gods of Avlis draw their magical power from some separate source, which is different from that which sorcerers and wizards derive their magics. "God Magics" are exact mirrors of mortal magics. The same spells exist in both, and even more that don't exist as mortal versions.
When a deity gives power to a cleric who worships him, the filtering of this magic down through the planes changes it. It is no longer considered "God Magic" at this point. The magics that clerics derive from their gods are classified much the same way as arcane magics, except that their source was ultimately the same as the God Magics at one point.