What does Grendel mean by "balance is everything"?

I think this is a yin and yang sort of thing. The balance of the dark and the light is perpetual. Form and function go hand in hand. In Grendel's case, he needs the "heroes" to destroy; this defines himself as Grendel. Similarly the heroes need a monster to fear and fight to be defined as heroes.

What does Grendel mean by "balance is everything"?