In the midst of prophesying destruction on Israel, Isaiah points ahead to the coming Messiah. He says, “The people who walked in darkness have seen a great light; those who dwelt in a land of deep darkness, on them has light shined” (Isaiah 9:2 ESV) When Simeon saw Jesus after his birth, the old man said, “[M]y eyes have seen your salvation that you have prepared in the presence of all peoples, a light for revelation to the Gentiles, and for glory to your people Israel” (Luke 2:30-32 ESV).
Similarly, when John was describing the incarnate Word of God, he wrote:
In him was life, and the life was the light of men. The light shines in the darkness, and the darkness has not overcome it. There was a man sent from God, whose name was John. He came as a witness, to bear witness about the light, that all might believe through him. He was not the light, but came to bear witness about the light. The true light, which enlightens everyone, was coming into the world. (John 1:4-8 ESV)
Jesus Christ, the Messiah, Immanuel – God with us, was and is the light of God, the light that God shined and continues to shine into the darkness of this world. As Jesus said, “I am the light of the world. Whoever follows me will not walk in darkness, but will have the light of life” (John 8:12 ESV)
But, what does it mean for Jesus to be “light”? What does “light” mean in this context? How do we know if someone is in the “light”? Jesus explained it to us earlier in the Gospel of John:
And this is the judgment: the light has come into the world, and people loved the darkness rather than the light because their deeds were evil. For everyone who does wicked things hates the light and does not come to the light, lest his deeds should be exposed. But whoever does what is true comes to the light, so that it may be clearly seen that his deeds have been carried out in God. (John 3:19-21 ESV)
The person walking in the light is recognized by their deeds, by the way that they live their life. This is very similar to what Jesus said during the Sermon on the Mount:
You are the light of the world. A city set on a hill cannot be hidden. Nor do people light a lamp and put it under a basket, but on a stand, and it gives light to all in the house. In the same way, let your light shine before others, so that they may see your good works and give glory to your Father who is in heaven. (Matthew 5:14-16 ESV)
While earlier we saw that Jesus himself was the light, we now see that we are the light when our lives and actions (our good works) glorify God.
Likewise, Paul exhorted his readers to live as light:
Let no one deceive you with empty words, for because of these things the wrath of God comes upon the sons of disobedience. Therefore do not associate with them; for at one time you were darkness, but now you are light in the Lord. Walk as children of light (for the fruit of light is found in all that is good and right and true), and try to discern what is pleasing to the Lord. (Ephesians 5:6-10 ESV)
Notice that in this case, Paul gives the positive exhortation to walk as children of light, which he explains as being found in all that is good and right and true. But, Paul also gives us a negative example. “Empty words” is a trait of the disobedient, not the children of light, who bring glory to God by their actions.
Jesus was the light and is the light, and as Immanuel – God with us, he continues to shine through us so that we also live as children of light, bringing glory to God through our actions.