so how was there a balance between good and evil?
Your equating good and evil to positive and negative but they are not the same thing.
Good and evil are concepts of mankind based on the actions of mankind. Our freewill allows us to chose our actions.
Positive/Negative are universal opposing conditions which must always give of themselves to the other out of their imbalance in order to remain balanced.
Thats gods law for the universe in order for it to exist in which it has no choice.
Evil doesn't give of itself for good..,.
Man should give of himself to man. Thy brothers keeper, love your neighbor as yourself etc...
When man choses to disobey the natural law as he does through greed,lust,selfishness etc... He creates imbalance in himself and others. The penalty for this is in equal measure as the offense in order to void mans imbalance.