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.
Good and Evil
Light or Darkness?
Darkness forms in response to the light God created, but God isn't darkness. Evil forms in response to the peace that God created, but God isn't evil.
Darkness Did Not Comprehend It
Why did it get dark at the end of the 1st day? It wasn't absence of light, it was obstruction of light by the corruption which resulted from the appearance of light. It needed a new name: night.
The Milk of the Word
We find that there are passages of scripture which, though appearing to be metaphorical, describe actual physical conditions or chemical reactions. These misunderstood passages are dismissed as flowery poetic language.If a baby needs milk to survive before it can tolerate solid food, has this been patterned after the processes which took place on the first and second days of the creation of the universe?
January 31st
God could have made a perfect creation from nothing, he didn't. Instead God used water. The result is a creation where there's continuous struggle between light and dark. Why? So that we may have free will.
What was the Darkness?
The darkness that existed in the beginning (Genesis 1:1) was the darkness of a complete absence of light. The darkness that came at the evening of the first day was a created darkness.