Now there was a Pharisee named Nicodemus, a leader of the Jews. He came to Jesus by night and said to him, 'Rabbi, we know that you are a teacher who has come from God; for no one can do these signs that you do apart from the presence of God.' Jesus answered him, 'Very truly, I tell you, no one can see the kingdom of God without being born from above.' Nicodemus said to him, 'How can anyone be born after having grown old? Can one enter a second time into the mother's womb and be born?' Jesus answered, 'Very truly, I tell you, no one can enter the kingdom of God without being born of water and Spirit. What is born of the flesh is flesh, and what is born of the Spirit is spirit. Do not be astonished that I said to you, "You must be born from above." The wind blows where it chooses, and you hear the sound of it, but you do not know where it comes from or where it goes. So it is with everyone who is born of the Spirit.'
(Church in Wales Lectionary, New Revised Standard Version)
Nicodemus a Pharisee (and probably a member of the Sanhedrin) comes to Jesus on the quiet. Opposition to Jesus is already growing so perhaps he can't afford to be seen. He comes to learn more about Jesus and his message, though notice that he doesn't actually ask a question.
The phrase "being born from above" is often translated as "being born again" and can cause problems. Some Christians exepect others to be able to quote the exact date and time they were "born again in the Spirit". One theologian (W. Brents) pointed out "The mist and fog that has been thrown around this verse envelopes it in darkness thick as that with which God cursed the land of Egypt." No Christian should look down on another Christian - it is God who judges!
Jews expected to be admitted into God's Kingdom because they were Jews, but Jesus says this is not enough. We may not understand exactly what being 'born again' means (some think we are born again through baptism; some through the Word of God; and others through the Holy Spirit), but what we do know is that we are not born again in a spiritual sense because of something we do, but because we open ourselves to God's Spirit and allow Him to work in us.
Holy Spirit, breath of God,
work within us that which is pleasing
so that we may grow in faith
and live out this life in faithfulness
as members of the Kingdom of God.
If you want to find out more about Nicodemus here is a site that looks at him: