I've always treated it more like spooling the magic up inside the wizard, ready to cast. Which is pretty much the same thing as 3.X where (as someone else already mentioned) you're pre-casting minus the final triggers, and it's those triggers that are the spell requirements when cast in play.

Either version of it also explains why intelligence is the key stat, since the mental discipline required is the difference between wizards and sorcerers. Sorcerers rely on their inner power to generate the magic effects, and only need to know what triggers that release. Divine casters don't need any of that because the magic is from an external source to begin with.