Do you hate? The most powerful hate is not born out of ignorance or prejudice or a perceived threat. Those three are fear in disguise. The fury that fuels my corps ignites from personal pain. Those whose lives were ravaged by greed, lust and control wield the crimson light. The rings replaced our damaged hearts. They beat for them. And they keep us alive only to hate. But at least we live.
I have hate. It is a burning fire inside me that I cannot quench. It is a force that I struggle at all times to bring to heel lest it bring me low in my haste. It preoccupies my thoughts and forces me to do things that I otherwise might not. It is my greatest weakness but also my greatest strength. It is not the best trait for a warrior, but it is all I have left... and it is enough.
Everyone will tell you to let it go and move on, but don't! Instead, let it fester and boil inside of you! Take these feelings and lock them away. Let them fuel your actions. Let hate be your ally, and you will be capable of wonderfully horrid things!
However you look at it, in these books "power" tends to be an expression of the essential nature of the person or being whose power it is. On those occasions when we've seen LordFoul act directly, he seems to exert the withering force of pure scorn. IMHO, that's pretty intense.
Revenge is the prime ingredient in the fountain of youth. I've kept myself alive for hundreds of years with a steady diet of jealousy and hate, awaiting the day when I will eclipse your family's thieving reputation.