Jesus here may be likening himself to the sun in the sky. If he is, the first suggestion that comes out of this illustration is that Jesus belongs to the heights. He is from above. His native home is heaven. He is the light because he is the eternal God. In the beginning, he who dwells in light created the natural light. It is straightforward to deduce that because his eternal home was heaven, Jesus is superior to us.
The second detail to note about the sun is that it is separate from the earth. Because of the distance it is from the earth, the sun is not contaminated by the pollution of earth. Jesus is like the sun in this regard in that he is unaffected by the sin of the human race. Instead, he is always holy, without sin. Yet although the sun is detached from the earth, its influences affect the earth. The same is true of Jesus.
Thirdly, the sun is a picture of strength. In Psalm 19, the sun is likened to a strong man about to run a race. It needs strength, we can say, because of the several activities it has to perform. For example, it has to dispel the darkness of the previous evening; in some places, it has to melt the frozen waters and ground; in other places, it is needed in order for crops to grow. We can see how each of these activities of the sun depicts the work of Jesus, both with regard to conversion and to progress in the Christian life.
Fourthly, the sun gives us the ability to see where we are going. Without the sun, there would be permanent darkness and life would be nothing but confusion. Jesus gives to us the ability to see the path ahead.
Fifthly, this statement by Jesus, that he is the light of the world, highlights three crucial features. One is stated in his use of the definite article ‘the light’ – he is the exclusive Light. He is not a light, one of many possible deliverers. He alone can do what is needed for salvation. Moreover, he is the universal light, not just for Israel, but for all the peoples of the world. And he is the permanent light, who will never be replaced.