Jesus says here "I am the light of the world". Jesus talks about this world as being in darkness.

Jesus provides light to the world by appearing in it, since he is the light.

If you are lost in a dark cave you can get out if someone from outside comes in with a torch and illuminates the way. This world is like a dark cave where everyone is covered by the darkness of their sins.

Jesus shines the light of truth on mankind and lets them see what they are, how lost they are.

Jesus shines the light also to show us the way to get to Heaven by following him who is the light.