What does it mean that the light shines in the darkness (John 1:5)?

from the old testament

• In Psalm 27:1 David proclaims, “The Lord is my light and my salvation; whom shall I fear?” David was beset by troubles throughout his life, including being hunted by King Saul. But no matter how dark life became, David was always aware that the Lord was with him. David knew the light of the Lord would overcome any evil against him.
• In Psalm 36:9, David describes how God brings light into the life of those who trust Him: “For with you is the fountain of life; in your light do we see light.” This is contrasted with the unrighteousness of those who have “no fear of God” and who practice unrighteousness (Psalm 36:1–4). The darkness of such unrighteousness will not flourish (Psalm 36:12). God illuminates the life of those, like David, who follow Him.
• Isaiah 9:2 prophesies the coming of Christ using the metaphor of light: “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.” Without Christ, the world would be a dark place, without hope. Christ’s atoning sacrifice and resurrection defeated the darkness of death.

from the new testament

• John 1:5 is preceded by John describing Jesus as God, the One who was from the beginning, the Creator (John 1:1–3). John then writes, “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” (John 1:4–5). Jesus came as light to a dark and searching world. He is stronger than the forces of evil and has overcome death.
• First John 1:5 tells us “that God is light, and in him is no darkness at all.”
• Believers have the light of Christ within us. Matthew 5:14–16 records Jesus’ teaching that we should let our light shine: "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."
• When believers let their light shine, it gives glory to the “Father of lights” (James 1:17).
• Our light can’t shine if it’s hidden by the darkness of sin, as 1 John 1:6–7 explains: “If we say we have fellowship with him while we walk in darkness, we lie and do not practice the truth. But if we walk in the light, as he is in the light, we have fellowship with one another, and the blood of Jesus his Son cleanses us from all sin.” Though everyone has a sinful nature because of the light of Christ within us, believers do not live in persistent sin.
• Ephesians 5:8–9 confirms the changed life of those who put their faith in Christ: "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).” When we put our faith in Jesus as Lord, we become filled with His light.

implications for today

Many children fear the dark. As adults, we may no longer fear physical darkness, but the darkness of sin definitely affects us. From sickness, disease, death, difficulties, thorns, consequences of sin, fear, and so much more, it is clear that sin definitely affects us. Spiritual darkness is more terrifying than the fear we felt as children as it separates us from God and leads to our destruction. But for believers, the light and salvation of God within our lives means we never have to fear (Psalm 27:1) even though we still live in a sin-stricken world because we walk according to the ways of God (Psalm 119:105). Christ has overcome the darkness of sin and death (1 Corinthians 15:54–58). Through Him, we have the promise of eternal life. We know when we sin, we can confess our sins to Him, and He will forgive us (1 John 1:9). The mercy, grace, and love we have been shown should compel us to let our light shine so we can glorify our Heavenly Father to others. How we live and how we love others reveals the light of Christ in us (1 John 2:8–11). Are you sharing the gospel with others? Are you using your resources and your abilities to advance God’s kingdom? God uses us to bring those living in darkness into the light. And the best part? Christ’s light can never be extinguished (John 10:28).