It seems to me that through various points made in this thread that while soulstones/crystals are a repository of ancient power, they're not so much there to give you the power itself to use the abilities. Rather they act as an aetheric conduit or focus (much like how one needs a focus to do conjury/thaumaturgy/etc) to control or at least focus the power you've come upon into a usable form.
The Paladin soulstone seems to draw out holy power within you, Dark Knight focuses your inner darkness into power you can channel through emotion, Warrior gives you power to focus your Inner Beast into a berserker form, White Mage seems to give you enough focus to use Succor, Dragoon allows you to control the blood of the dragon...
The caveat that comes with all this new focused power is that you must learn to control it yourself, the soul crystal cannot do it for you, it's merely there so you have the ability to access this power. Fail and any number of bad juju will happen to you depending on what power you're drawing on.
The Paladin soulstone seems to draw out holy power within you, Dark Knight focuses your inner darkness into power you can channel through emotion, Warrior gives you power to focus your Inner Beast into a berserker form, White Mage seems to give you enough focus to use Succor, Dragoon allows you to control the blood of the dragon...
The caveat that comes with all this new focused power is that you must learn to control it yourself, the soul crystal cannot do it for you, it's merely there so you have the ability to access this power. Fail and any number of bad juju will happen to you depending on what power you're drawing on.
