Whereas arcane magic originates in the Elemental Chaos, the source for divine magic lies with the gods. When a mortal cleric casts magic, he receives power from the gods. Whether the gods themselves emanate this magic, or gather it from within the Astral Sea is unknown.
Whereas arcane magic must be “filtered” through the Five Founts for safe use by mortals, the gods serve this function for all divine magic. No mortal creature could ever hope to control divine magic without the aid of the gods; any mortal foolish enough to make the attempt would undoubtedly vanish in a bolt of lightning or flash of flames.
Arcane magic filters through the world without intent or demand. Whether spellcasters manipulate the flows of magic or not, these flows exist. The forces of arcane magic care nothing for mortals or other creatures. Divine magic, on the other hand, only appears at the direct intent of the gods (or their intermediaries). If a cleric or paladin heals a wound or banishes an undead monster, they are able to do so because their god permitted it to happen. All divine spells evolve from a specific intent, even in circumstances where the intent seems uncertain or obscured. Divine magic does not manifest in the mortal world unless a god first wills it to do so.
There are times, of course, where mortals misuse divine magic for selfish reasons, or without understanding the consequences. For the most part, the gods do not police or censor how their worshippers use divine magic. In particularly egregious cases, an angel of retribution or vengeance might appear and destroy a mortal spellcaster for misusing divine magic. Overall, such blatant shows of displeasure remain rare. The gods have better things to do with their time than observe how every single cleric or other divine spellcaster makes use of their powers. There seems to exist an underlying assumption that the gods grant divine magic to their followers with the assumption these followers will use such gifts appropriately. If the gods determine otherwise, they are more likely to eradicate the offender rather than merely cut off magic from the individual.
Divine magic possesses another unusual trait that separates it from any other form of magic. Divine magic is especially attuned towards healing wounds and curing illness, among other uses. This is not to say that other forms of magic cannot heal or cure, but divine magic seems especially suited to these purposes. By contrast, extremely few arcane practitioners have any magical capability to heal injuries.