Frank pretty interesting topic ...
I grew up in a seventh day adventist environment, while at one point in my mid teens that I considered the option to study Theology and the Churches Fundamental Beliefs. Basically considering becoming a pastor or a minister. I am now agnostic. So here goes ... and I could be wrong on the context (my religious knowledge is a little rusty), Matthew or someone with a more active knowledge can clarify any of my wrongs.
In the old testament life was just that, life; it wasn't until the temptation of Adam and Eve that the introduction of pain perhaps even death (Genesis). God/Creator allowed for Adam and Eve to make a choice, it was their free will.
God's integraty ... “My covenant will I not break, nor alter the thing that is gone out of my lips”. I don't think a line like that shows weakness or without choices. If you're a Christian you would say that unwavering strength.
Some sectors of Christianity believe that Satan does not have a superior power or authority. He is absolutely dependent upon the cooperation of a human being who will empower him with the authority God gave them. That he is indeed weak and preys on the sin and weakness within man and not the other way. Lucifier/Satan was told to protect the Adam and Eve, yet he corrupted it due to his own desires and jealous of Man (Who was the image of God and were the authority over Earth). Its after Genesis and before Eve had children that most Christians believe Lucifier turned against God.
As for the light and darkness (non religion but light theory), what about this messy theory ... that dark is the by-product of having absorbed all light, so if there is no light there is no darkness. To have black it has to absorb light (or all shades of the primary colours). So if you've got no light then black can't absorb anything and hence it does not and can not exist. As for the Yin Yang theory ... black or darkness have no control over light, that light in itself controls everything, including the existence of darkness.
But then you get into the messy area ... that the human eye only sees certain elements (or wave lengths) of light, the spectrum of light that the human eye can not see is called "Ultraviolent" or Black light. Eek
If we applied that theory to good and evil, than to experience evil (Dark) you must first have good (Light), but no matter how much you see there is always the invisible part that is truely and utterly evil (Black Light).
In Japanese culture, white represents symbolizes serfdom, youth, and naiveté. While black represents a symbol of nobility, age, and experience.
I don't believe in the existience of someone being one way or the other, to be purely good or evil.