Sermon Help: 'Junior' has to do it all again?

You are not going to believe this: The reading in the lectionary for Sunday (and the text assigned for me to preach) is John 3:1-18: Being Born Again!

Now, 'Junior' went through it once last on Monday. And apparently, he has to do it all again sometime soon! If not, Jesus says that he will not see the kingdom of God, which is a sobering thought.

Here is the exchange:

Jesus answered him [Nicodemus], 'Truly, truly, I say to you, unless one is born again he cannot see the kingdom of God." Nicodemus said to him, "How can a man be born when he is old? Can he enter a second time into his mother's womb and be born?"

Good point, Nicodemus.

So... Some Questions:

• What is the connection with 'seeing the kingdom of God' and 'being born' a second time?
• Is it a metaphor? How does the metaphor work? What is Jesus referring to?
• How is birth a good image of becoming a Christian?
  
• Why should we 'not marvel' at this? (it seems marvelous to me!)

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