Although we rarely talk about or think about death, most of us are pretty sure that we will live somewhere forever when we die. I say that because that's what most statistics say we believe. The vast majority of the Western world believes in a heaven and most of the Eastern world believes in some sort of re-incarnation where we come back as something else or someone else. The common denominator in the Western world and the Eastern world is this...both the Western world and Easter world believe pretty much the same thing. How you live on this side of life, determines what you get on that side of life.
Nicodemus had amazing credentials. He was talented, a good communicator, generous, religious he knew the bible, he had a ferocious prayer life and millions of good deeds. Beyond that he also had humility and a respect for Jesus. If anyone on the earth had an argument for getting into heaven, it was this guy. All of that said, Jesus totally overlooks all of Nicodemus's credentials and tells him that it's not enough, be must be "Born Again."
Being "Born Again" is not something that you can do yourself. It's not a list of deeds that we can accumulate and hand in to receive "New Birth"; rather it is a work of God. Saying we're born again does not make us born again again, just as much as saying someone is a millionaire makes them a millionaire.
So, how does someone become "Born Again"? Jesus answers this for us in John 3:13-15. In these verses, Jesus compares his death on the cross to an event that happened in the Old Testament. In Numbers 21, God punished Israel for their complaining by sending venomous serpents to attack them. Then, to build their faith, God told Moses to make a golden serpent and lift it up. As people would look at that serpent, they would be miraculously healed. In the same way, we have a poison called sin. Christ tells us that as we look at the cross and believe that the penalty for sin was paid for by Christ on the cross; that "believing" is how one experiences a New Birth. Its not what we do, it's seeing and believing what has been done for us that gives us eternal life. Its not paying for all of our bad deeds that gets us eternal life, its seeing and believing in the one who had the riches to pay for our bad deeds. Jesus Christ our Lord.