Creation was corrupted before Adam and Eve sinned in the garden of Eden. It was created in a corrupted state in order to manifest free will. We can prove it using a process we call deductive questioning.
Light = Good; Darkness = Evil
The parallels between light and good vs. darkness and evil are stated throughout scripture. Isaiah laments people who try to make you believe that good is evil and evil is good, and who put darkness for light.
Separation is a scriptural doctrine which is generally thought of in terms of Christians holding themselves apart from the rest of the world and avoiding worldly distraction which can lead us into sin. There's more to it than that.
Good and Evil
The purpose of creation is to separate good from evil. A reasonable question is: Why were they mingled together in the first place? If God is good, then the evil had to be created from good. The sinless became sin.
There are two issues that help us to understand the reason for why we were created with free will and how this is even possible given the nature of God as pure and holy, not to mention omnipresent and omniscient.
Relationship of Cause and Effect
Understanding cause and effect, the essence of logic and reason, is critical in successfully deducing how the Bible can account for all of the physical evidence and our empirical observations of the universe.
Origin of Gender
The Holy Trinity is the origin of gender. God refers to himself as male, Alpha, the Father. Jesus Christ, the begotten, is the Son. Simple deduction gives the gender of the Holy Spirit, Omega, to be female.
A Biblical Narrative for Physics
The reason and purpose of creation form the basis of narrative which allows us to account for all physical evidence and empirical observations within the context of 6 day creation, the fall and the fulfillment of prophecy.
The Big Picture
We can parse the difference between hell and the lake of fire because we've laid out the broad narrative of scripture, the conceptual backbone of the Bible, a theme which weaves together the law, prophets and the gospel.
Purpose, Reason and Function
The war in heaven which led to Satan being banished to Earth isn't some terrible mistake that happened. It's the working out of God's will with the eventual goal of a place where he dwells in perpetual light with his people.