from GotQuestions.org [https://www.gotquestions.org/God-is-light.html]
“God is light,” says 1 John 1:5“This is the message we have heard from him and proclaim to you, that God is light, and in him is no darkness at all.” (ESV). Light is a common metaphor in the Bible. Proverbs 4:18“But the path of the righteous is like the light of dawn, which shines brighter and brighter until full day.” (ESV) symbolizes righteousness as the “morning sun.” Philippians 2:15“that you may be blameless and innocent, children of God without blemish in the midst of a crooked and twisted generation, among whom you shine as lights in the world,” (ESV) likens God’s children who are “blameless and pure” to shining stars in the sky. Jesus used light as a picture of good works: “Let your light shine before others, that they may see your good deeds” Matthew 5:16“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.” (ESV). Psalm 76:4“Glorious are you, more majestic than the mountains full of prey.” (ESV) says of God, “You are radiant with light.”
The fact that God is light sets up a natural contrast with darkness. If light is a metaphor for righteousness and goodness, then darkness signifies evil and sin. 1 John 1:6“If we say we have fellowship with him while we walk in darkness, we lie and do not practice the truth.” (ESV) says that “if we claim to have fellowship with him and yet walk in the darkness, we lie and do not live out the truth.” Verse 5 says, “God is light; in him there is no darkness at all.” Note that we are not told that God is a light but that He is light. Light is…His essence, as is love 1 John 4:8“Anyone who does not love does not know God, because God is love.” (ESV). The message is that God is completely, unreservedly, absolutely holy, with no admixture of sin, no taint of iniquity, and no hint of injustice.
If we do not have the light, we do not know God. Those who know God, who walk with Him, are of the light and walk in the light. They are made partakers of God’s divine nature, “having escaped the corruption in the world caused by evil desires” 2 Peter 1:4“by which he has granted to us his precious and very great promises, so that through them you may become partakers of the divine nature, having escaped from the corruption that is in the world because of sinful desire.” (ESV).
God is light, and so is His Son. Jesus said, “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“Again Jesus spoke to them, saying, ‘I am the light of the world. Whoever follows me will not walk in darkness, but will have the light of life.'” (ESV). To “walk” is to make progress. Therefore, we can infer from this verse that Christians are meant to grow in holiness and to mature in faith as they follow Jesus (see 2 Peter 3:18“But grow in the grace and knowledge of our Lord and Savior Jesus Christ. To him be the glory both now and to the day of eternity. Amen.” (ESV)).
God is light, and it is His plan that believers shine forth His light, becoming more like Christ every day. “You are all children of the light and children of the day. We do not belong to the night or to the darkness” 1 Thessalonians 5:5“For you are all children of light, children of the day. We are not of the night or of the darkness.” (ESV). God is the Creator of physical light as well as the Giver of spiritual light by which we can see the truth. Light exposes that which is hidden in darkness; it shows things as they really are. To walk in the light means to know God, understand the truth, and live in righteousness.
Believers in Christ must confess any darkness within themselves – their sins and transgressions – and allow God to shine His light through them.
Christians cannot sit idly by and watch others continue in the darkness of sin, knowing that those in darkness are destined for eternal separation from God. The Light of the World desires to banish the darkness and bestow His wisdom everywhere Isaiah 9:2“The people who walked in darkness have seen a great light; those who dwelt in a land of deep darkness, on them has light shone.” (ESV); Habakkuk 2:14“For the earth will be filled with the knowledge of the glory of the LORD as the waters cover the sea.” (ESV); John 1:9“The true light, which gives light to everyone, was coming into the world.” (ESV). In taking the light of the gospel to the world, we must by necessity reveal things about people that they would rather leave hidden. Light is uncomfortable to those accustomed to the dark John 3:20“For everyone who does wicked things hates the light and does not come to the light, lest his works should be exposed.” (ESV).
Jesus, the sinless Son of God, is the “true light” John 1:9“The true light, which gives light to everyone, was coming into the world.” (ESV). As adopted sons of God, we are to reflect His light into a world darkened by sin. Our goal in witnessing to the unsaved is “to open their eyes so that they may turn from darkness to light and from the power of Satan to God” Acts 26:18“to open their eyes, so that they may turn from darkness to light and from the power of Satan to God, that they may receive forgiveness of sins and a place among those who are sanctified by faith in me.” (ESV).
In Christian theology, the doctrine of divine simplicity means that God is not composed of parts or attributes that are distinct from His essence. God is what He has. In other words, God’s attributes are not added to His essence but are rather ways of talking about the one simple (undivided) essence of God. The phrase “God is light” from 1 John 1:5 is often understood metaphorically to refer to God’s holiness, righteousness, goodness, etc. In this sense, “light” describes God’s essence, but it does so in a way that is meant to encapsulate His divine simplicity, not to add to or divide His essence.