They loved darkness rather than light

“This is the verdict: Light has come into the world, but men loved darkness instead of light because their deeds were evil. Everyone who does evil hates the light, and will not come into the light for fear that his deeds will be exposed.” John 3:19-20
Light is a theme throughout John’s gospel and letters. He uses as as a symbol of goodness and spiritual truth. Jesus, being the source of all that is good and all that is true, is the light of the world (John 1:9). Darkness then, is not the opposite of light, but the absence of light. When light comes into a dark place, it shows clearly what is there. Before, you might have been guessing at what something is, by touch or smell. But in the light, you can see it and easily identify it.
When it comes to spiritual things, people would rather be kept in the dark as to the depravity of their souls. When we compare ourselves with other people, we can feel like we’re ‘not that bad’. We can always find someone who is guilty of a worse, or different, sin. But when the light of Christ shines on us, we see all of our sins for what they are.
There are two responses in this situation. One, is if we submit to the conviction of the Holy Spirit, and repent and turn to God. The other is to seek to continue with what we are doing, and reject the light so that we don’t feel as depraved as we are. This is the crux of it: people don’t want to be accountable to God. It isn’t that they can’t believe – they deliberately refuse to, because they don’t want to change.