Why was the lamb slain at the foundation of the world? So that light could become darkness, good could become evil, the sinless could become sin, and we could have sentient life with free will.
The Lamb of God
The Light of Life
Things on Earth are patterned after things in the heavens. God has withdrawn his presence from the world and dwells in a realm of light, while we are here on Earth toiling through an ever encroaching darkness.