John 3:19

And this is the judgment, that light is come into the world, and men loved darkness rather than light; for their works were evil.

Christ had just mentioned that he had not come to judge the world in any such manner as the hierarchy expected; but, to be sure, there was a judgment going on already, a judgment precipitated by the dramatic appearance of the Messenger of the Covenant who had suddenly come to his temple. It was a judgment required by the dazzling Light of all nations in the first advent of our Lord. As men reacted to that Light, their fate was sealed. That moral judgment could not be put off until some distant cataclysm; it was in full progress while this interview with Nicodemus was going on.

This verse forever lays to rest the conceit that unbelief is an intellectual problem; on the contrary, it is basically a moral problem.

Men have loved darkness rather than light; for their works were evil ... Jesus thus revealed that loving darkness rather than light is due, not to intelligence or learning, but to evil works. In an age when infidelity masquerades under all kinds of disguises, especially that of intelligence and erudition, this is an extremely important verse. Its very first application, of course, was to the Pharisees and Sadducees of Jesus' time, who pretended such a thorough knowledge of the Scriptures, but who, in the last analysis, knew nothing at all about them. Yes, there was a sense in which such people knew the Scriptures; but, unless knowledge is held in good and honest hearts (and in their case, it was not), then even knowledge itself becomes darkness in the soul.

This verse still applies to unbelief, because the moral judgment going on when Jesus spoke to Nicodemus is still in progress. Believers in Christ are not judged, being safe "in him"; but unbelievers have been judged already by their rejection of the only hope of the world.