Big Picture: “The dominant focus in the apparent detour in verses 13 -29 - the detour away from "I am the light of the world" - is that the testimony and the judgments of Jesus are true and authoritative because of his relationship with God the Father. At least seven times in this passage, Jesus points to the fact that he is from the Father, and speaks on the authority of the Father, and is going to the Father, and does nothing on his own. Jesus claims, in other words, that his authority is not owing to any human origin. It's owing to his relationship with God the Father.”  (John Piper)

1: Jesus is the light of the world. Whoever follows Jesus will never walk in darkness, but will have the light of life (12)

2: The validity of Jesus’ solitary witness questioned (13-20)

3: The origin of Jesus’ authority (21–30)