The thin line between 2 different thing

I was flipping among the channels on Astro the other day, and I came across this movie called "Whisper" (ok, not that sanitary pad's brand). It's almost come to the end of the movie already but somehow the scene just caught my attention.

The lines go like this:

Roxanne: what are you?
David: I'm angel.
====
David: I'm just getting started here. Poor Roxanne, she thought I was an angel. You can't kill an angel.
Max: a demon, maybe.
David: Ah, but a demon is but an angel who fell. Like you are gonna fall, Max. Don't look so sad, killer. You're on the winning team now. No commandments. No guilt. I was sent for those that are desperate...I come to them when they are weak. When their lives are hopeless. When those they love reject them. I come to them, whisper in their ear, and I can be very convincing.
Max: Why, David? Why all this?
David: Casting for souls, Max. That's what I do.
Max: And me? What do I do?
David: You're as weak as the rest of them. So, be a good boy and put the gun to your head. Do it or hear my voice every moment of your life. It was a good game, Max.

Well said.

What's the difference between angel and demon? Likewise, what's the difference between good and evil; or winner and loser? What determines the answer?

The light cannot exist without the company of shadow and darkness will be broken by a shed of light. Similarly, isn't it so that falling and rising are connected?

But I guess we get to choose the side we want.

Although we can't stop ourselves from falling sometimes (so that we get to rise up again), but don't dwell with darkness or stay in the shadow for long. It drowns, and sinking just isn't the answer. Why not? Because the negative has no life. Instead, it takes away the reason of living.

Believe me, I've seen that and I'm glad I pulled it through before it sucked me in.

Cast the light and let it be the guidance, not the shadow.