How I would define "Being" and "Non-Being"

Being would be: I am, I think, I do, I am alive, I am consciousness, I observe, I might have a physical body.

Non-Being would be: I'm asleep, I am dreaming,  I am drifting, I am renewing, I may or may not have a physical body.

Why is understanding this important?

Because Time and Space are temporary. Having a physical body is temporary (relatively speaking) understanding that Being and non-being are the only things we can count on being there forever as souls.

Enlightenment exists in Being and Non-Being.

Time and Space are relatively temporary variables.

So, to become enlightened you focus on Being and Non-Being as the permanent state of the universe as a soul.