In the third chapter of John, we find the heart of Christianity.  Some things we may debate, but there is one fundamental that cannot be debated, and that is that you must be born again.  Nicodemus, a Pharisee who was a leader of the Jews, came to Jesus by night.  He was curious about Jesus, but didn't want to come to Him when a lot of people might see him.  We cannot come to Jesus in secret.  We must openly confess Him to the world.  Nicodemus acknowledged Jesus as a teacher sent from God.  He recognized that no one could perform the miracles Jesus had without God's power.  It is not enough that we recognize Jesus as simply a teacher sent from God, an extraordinary man, or anything less than the Only Begotten Son of God.  There are those who acknowledge Jesus as being a prophet, a good man, and a historical figure, but they see Him as only a man.  We must acknowledge Him as the Son of God if He is to be our Savior.   Jesus' response to Nicodemus in verse three was, "Verily, verily, I say unto thee, Except a man be born again, he cannot see the kingdom of God."  There is not a should be or might be or could be, but a must be.  When people say there is any other way to a relationship with God, they are simply wrong.  Nicodemus asked how a man that is old could enter a second time into his mothers womb.  Jesus responded to him in verse five, "Verily,verily, I say unto thee, lest a man be born of water and of the Spirit, he cannot enter the kingdom of God."  This does not mean we must be baptized.  We are born physically, of the water, and we must be born again, of the Spirit.  Then He continued in verse six, "That which is born of the flesh is flesh, but that which is born of the Spirit is Spirit."  When we accept Jesus as our Savior, we become of the Spirit, not of the flesh.  We have a new nature, based on doing God's will, not the will of the world.