Here, this might help. =)
http://www.d20srd.org/srd/combat/action ... CastaSpell
Casting Time wrote:
Most spells have a casting time of 1 standard action. A spell cast in this manner immediately takes effect.
I don't remember where I got this. It might have been a DnD fiction, but it's always sort of hung around in the back of my mind. Notice, preparing spells (the current nomenclature) used to be memorizing spells;
So, here's how I remember it being explained. Arcane spells are long and complicated forumlae, typically. That's why wizards require spell books. When a wizard prepares a spell, they are essentially 'casting' the spell, except for a few missing 'ingredients' to the formula. IE the words that are 'chanted' or intoned when actually releasing the spell. The act of preparing spells draws upon the energy reserves of the caster, which is why they require a certain amount of rest before doing so. This is also why wizards gain bonus spells for a high intellect. They're capable making more efficient formulae, thus drawing on the personal reserves of the wizard. Similarly, as a wizard increases in level, they increase in capability to draw on arcane energies. Able to store more within themselves (similar to how warriors gain hit points. They're able to take more physical punishment).
This is also why scrolls and potions require the casting of a spell. The spell is stored either in material components for a potion (eye of newt, stare of a basilisk, sound of a harpy's voice, etc), or in arcane writings that contain the energy of the spell, which are released from the parchment when key words from the formula are spoken.
Bards and Sorcerers don't prepare spells, because they use sheer force of will (IE Charisma) to form the arcane energies. They don't use formula. They instinctively know how to form the arcane energy into the effect they desire. The more Charisma, presence of personality, they have, the more spells they can cast.
I imagine I could interpret this into divine format, as well, but it probably isn't necessary. <.<