She just smiles and settles into her teaching mode.
"So - the classic philosophy is that the Force has two sides, or modes, or states of being. The Light, represented by harmony, peace, and compassion, and the Dark, represented by passion, anger, and aggression. It's..." Her gaze goes briefly distant. "If you have your eyes closed... The only thing you can see about your surroundings is if it's light or dark out. And - that is a fairly basic division of the Force, if only because those are the two roads people have trod for millennia, leaving all other potential paths to become overgrown. But... It's not all there is to the Force." Quietly: "When I died, it was like my eyes opened for the first time, and I saw color. I saw everything the Force is. My vision - closed down a bit, when I manifested as a ghost. But that's something important to keep in mind, Rey. Light or dark - it's all the same Force. The same thing you're viewing, through two different perspectives."
"There's a lot of philosophy built up around the two sides. You could spend a lifetime reading and not reach a full understanding. The - typical understanding in my time, and possibly the typical understanding for your new friend, is that Jedi let the Force command them, and Sith command the Force. It's not so simple. Nothing is. The dark can consume and control. The light can be bent to a stubborn will. The Jedi weren't the only users of the light, and the Sith weren't the only users of the dark. And neither the Jedi nor the Sith really had room for love, or for a partnership with the Force."
"Classically, you keep the dark from eating you by commanding it. You come out of the dark by releasing emotion and attachment, though many Jedi held that once you'd turned to the dark once, it would forever dominate you. That's - not true." She wraps her arms around her knees. "I Fell from the light into the dark. When I used the light - I was emotional, I was attached, I loved and that love felt like basking in sunlight. When I used the dark - I'd never been so numb. Like everything I was had been swallowed by a black hole, leaving only a shell. Love brought me out of that hole, and into a world beyond light and dark."
"Your friend probably struggles with fear and anger. Most people haunted by the dark do. Fear... It's something that lurks behind every emotion. Fear of losing what you love. Fear of other people growing more powerful than you. Fear of sorrow. Fear of joy, even. And anger - there's many things to be angry about. I could spend a hundred years drowning in fury, and never think of all the things that deserve anger. Those aren't bad emotions. Not on their own. Fear tells us that danger might exist. Anger says this isn't fair."
"The problem is when you let your emotions - your darkness - master you. I've walked that path before - I've killed in anger. Those are the deaths I regret the most. I've let my fear of loss cause my loss."
"Your friend... I suspect he's scared of the dark. As long as he can't master that fear - it risks consuming him."