Christ is a teacher, the enlightener, the guide, the Savior of humanity. He gives us light, that is, He gives us understanding, truth, and wisdom. So Jesus, as the One who brings the true knowledge of God, is the light of humanity. And when people tried to extinguish the light of men, darkness fell when Jesus was being crucified.
So the New Testament portrays Jesus as the personification of light, of divine illumination.
