John 1:5 says 'The light shines in the darkness, but the darkness cannot overcome it.'
The light that is referred to is Christ, who existed before time began. At the start of John 1 we are told that through Christ 'all things were made.' What was the ﬁrst thing Christ spoke into existence? Light! Before God spoke, 'darkness was over the surface of the deep' (Genesis 1:2), but by the power of His word, light came into being and it was no longer dark. God then created a vibrant world to be enjoyed, not just by Him, but by the people He created; a world where God and man could live in fellowship with one another. But when Adam and Eve sinned, God's voice was like a light that exposed the darkness of their sin and they hid from it. Fellowship between God and man was broken.
Thousands of years later, God spoke forth light again into a dark world- but this time the Word became ﬂesh and in 'Him was life, and that life was the light of men' (John 1:4). But in John 3:19&20 we read that 'Light has come into the world, but men loved darkness instead of light because their deeds were evil...and will not come into the light for fear that his deeds will be exposed.' Just like Adam and Eve, humans have a tendency to resist the light that reveals the darkness of their hearts. But, remember, 'the darkness cannot overcome the light', and 'God did not send His son into the world to condemn the world, but to save the world through Him (John 3:17). The light of Christ exposes our sin, but then sheds a glorious light on the way of salvation through faith in Christ: the light overcomes the darkness and fellowship with God is restored!