What did Jesus mean when He said, 'I am the Light of the World' (John 8:12)?"
Answer: “I am the Light of the world” (John 8:12) is the second of seven “I AM” declarations of Jesus, recorded only in John’s gospel, that point to His unique divine identity and purpose. In declaring Himself to be the Light of the world, Jesus was claiming that He is the exclusive source of spiritual light. No other source of spiritual truth is available to mankind.
There are two types of light in the world. We can perceive one, or both, or neither! When we are born into this world, we perceive physical light, and by it we learn of our Creator’s handiwork in the things we see. However, although that light is good, there is another Light, a Light so important that the Son of God had to come in order to both declare and impart it to men. John 8:12 records, “When Jesus spoke again to the people, He said, ‘I am the Light of the World. Whoever follows me will never walk in darkness but have the light of life.’” The allegory used by the Lord in this verse speaks of the light of His Truth, the light of His Word, the light of eternal Life. Those who perceive the true Light will never walk in spiritual darkness.
We take a candle into a room to dispel the darkness. Likewise, the Light of Jesus Christ has to be taken into the darkness of sin that engulfs the hearts and lives of those who are not following Him. That’s the condition behind having this Light—that we follow Him. If we do not follow Him, we will not have this light, this truth, this eternal life.
Physical light is necessary for physical life. The earth would certainly change very rapidly if there were no longer any sunlight. A forest full of trees with very thick canopies of foliage high above has very little plant life on the ground except for moss or lichen, which needs little sunlight. Plants will never move away from the light—they are said to be positively phototropic, drawn to the light. In the same way, spiritual light is necessary for spiritual life, and this can be a good test of our standing in Christ. The believer will always tend toward spiritual things; he will always tend toward fellowship, prayer, the Word of God, and so on. The unbeliever always does the opposite (John 1:5; 3:19–20) because light exposes his evil, and he hates the light. Indeed, no man can come into the true spiritual light of Jesus Christ, unless he is enabled (John 6:37).
Following Jesus is the condition of two promises in John 8:12. First, His followers will never walk in darkness, which is a reference to the assurance of salvation we enjoy. As true followers of the Light, we will never follow the ways of sin, never live in a state of continually sinning (1 John 1:5–7). Rather, we repent of our sin in order to stay close to the Light of the world. The second promise is that we will reflect the Light of Life. Just as He came as the Light of the world, He commands us to be “lights,” too. In Matthew 5:14–16 we see believers depicted as the light of the world. Just as the moon has no light of its own, reflecting the light of the sun, so are believers to reflect the Light of Christ so that all can see it in us. The Light is evident to others by the good deeds we do in faith and through the power of the Holy Spirit.
The emphasis here is maintaining a credible and obvious witness in the world, a witness that shows us to be faithful, God-honoring, trustworthy, sincere, earnest, and honest in all that we do. Also, we should always be ready to give an account of the hope that we have (1 Peter 3:15), for the gospel Light we have is not to be covered, but made obvious for all to see and benefit from, that they, too, may leave the darkness and come into the Light.