The deep had to be transformed in order to produce light. Formless became formed, empty became full, dark became light. However, this caused a new darkness: night. Not the absence of light, the obstruction of light.
Day > Night
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.