The next time you hear somebody making a distinction between the OT God and the NT God, you might remind them of this quote from John's gospel: those who believe are not condemned, but those who do not believe are condemned already.
We could deconstruct this passage by analyzing what "believe" means, what "condemned" means, particularly if the condemnation has already happened.
Further pondering on John's message could center on the nature of the judgment. Look at verse 19. Is he talking about a personal, individually-experienced punishment, or, is he talking about what happens to the whole community?
Come to think of it, is it even possible for an individual alone to be saved (whatever we might mean by saved)? Read verse 17 once more: God sent the Son in order that the world might be saved.
And read ahead in this Gospel: "I have have other sheep that do not belong to this fold," (10:16), and "In my Father's house there are many dwelling places," (14:2).
We are called by John to understand that God loves us, we who believe in Jesus. Can we further believe that God loves all?
Lectio Divina: John 3:21