People won't see the truth, people can't see the truth, until the Lord opens their eyes. That's a wonderful image for the effect that Jesus has. Think about what light does, how light functions. First, light illumines. It shows us what is there.
Light represents knowledge and understanding.
Like a bedside reading lamp, light enables us to gather the information on the page in front of us. We don't naturally know God or understand his ways. We only learn what he's really like and what he truly wants when we learn of him through Jesus, the light of the world. Jesus shows us the Father, and no one can know the full truth about God who does not know Jesus Christ. Second, light guides.