The Light

"And this is the verdict, that the light came into the world, but people preferred darkness to light, because their works were evil. For everyone who does wicked things hates the light and does not come toward the light, so that his works might not be exposed. But whoever lives the truth comes to the light, so that his works may be clearly seen as done in God. " - John 3:19-21

"Light" and "Dark" are two concepts that often represent "good" and "evil". From ancient eastern religions to modern-day space operas, they're used because they are easily understood by everyone. Jesus knows this, and frequents their use because he knows others will easily understand his message. In this particular case, Jesus is referring to "the light" in a pretty literal sense. He's telling Nicodemus that, despite his presence, people still are up to their evil deeds, still living their lives as they did before Jesus arrived. And they do so in a way that allows them to hide what they're doing from others - but not from God.

But there's also an underlying message - and prophecy - in the last part of this dialog. That "the light came into the world" - i.e. Jesus - but people preferred the darkness. And because of this, those people ended up murdering Jesus to try to keep their deeds from being seen.

What they didn't know was this light could never be extinguished. In fact, by trying to cover the light, they just made it brighter!