If I made that audacious claim, even (or especially) those closest to me would assume I was joking or insane. But when Jesus said it, He spoke the truth.
Think of the symbolism of light versus darkness.
Jesus is the embodiment and provider of understanding, clarity, guidance, life, new life, growth, health, warmth, transparency, righteousness, beauty, optimism, and hopefulness.
He makes it personal and gives a promise: “I am the light of the world. Whoever follows Me will never walk in darkness, but will have the light of life” (John 8:12).