Yeah, you can use X power by siphoning its essence to gain access to it — however it’s generally a shortcut, not a necessity.
So most light users would revere the light, pray and/or hold their faith towards their virtues to be granted their power, or something similar to such — whereas the Blood Elves simply TOOK that power from a being more inundated with that cosmic force, so that they could use it.
The Blood Knights used M’uru as a loophole.
Hence the dialog at the end of the Sunwell Plateau.
Dialog –
Prophet Velen says: The creature Entropius, whom you were forced to destroy, was once the noble naaru, M’uru. In life, M’uru channeled vast energies of LIGHT and HOPE. For a time, a misguided few sought to steal those energies…
Lady Liadrin says: Our arrogance was unpardonable. We damned one of the most noble beings of all. We may never atone for this sin.
Prophet Velen says: Then fortunate it is, that I have reclaimed the noble naaru’s spark from where it fell! Where faith dwells, hope is never lost, young blood elf.
Lady Liadrin says: Can it be?
Prophet Velen says: Gaze now, mortals - upon the HEART OF M’URU! Unblemished. Bathed by the light of Creation - just as it was at the Dawn.
The heart of M’uru disintegrates and flows into the Sunwell. The Sunwell reignites in a fount of blinding light.
Prophet Velen says: In time, the light and hope held within - will rebirth more than this mere fount of power… Mayhap, they will rebirth the soul of a nation.
Lady Liadrin says: Blessed ancestors! I feel it… so much love… so much grace… there are… no words… impossible to describe…
Prophet Velen says: Salvation, young one. It waits for us all Farewell …
The Blood Elves + The Light:
Thus now the Blood Elves less “take” or “siphon” such a force, and more-so channel into it — via the Sunwell, as with the Sunwell’s rebirth: The Blood Knights have engaged in a far more harmonious relationship with the Light, which they now channel directly through the Sunwell itself, wielding the Light in a healthy way, instead of taking, consuming, bending or dominating it.
Sources:
- Sunwell Plateau Raid
- Chris Metzen & Micky Neilson Pocket Star Books Lore Q&A Video Interview
- Ask CDev (Ask Creative Developmen ) Round 1