He who believes in him is not judged. He who doesn't believe has been judged already, because he has not believed in the name of the one and only Son of God.

 When John relates conversations that Jesus had with enquirers, he has a way of following a certain scheme. We see that scheme very clearly here. The enquirer says something ( John 3:2). Jesus answers in a saying that is hard to understand ( John 3:3). That saying is misunderstood by the enquirer ( John 3:4). Jesus answers with a saying that is even more difficult to understand ( John 3:5). And then there follows a discourse and an explanation. John uses this method in order that we may see men thinking things out for themselves and so that we may do the same. 