Jesus has a conversation with Nicodemus.
Nic: Jesus, we know you’re from God because you do these great signs.
Well, no. The Pharisees of the other gospels continually challenged Jesus’ authority and the source of his ‘powers’.
Jesus: You must be born again to see the kingdom of heaven.
“John” presents a Jesus very different from the other gospels. Gone is the apocalyptic preacher telling people to repent and do good works in preparation for a kingdom. For this Jesus, inheriting the kingdom of God requires a supernatural event.
Nic: I can’t exactly crawl back up into mom’s uterus.
Jesus: You must be born of the Spirit to inherit the kingdom of God.
Nic: How is that possible?
Jesus: You’re a rabbi and you’re ignorant of these things? I must be crucified and whoever believes in Me will have eternal life.
“John” gives us the more orthodox version of Christianity that we’re used to. A supernatural event is required to save a man who puts his belief in Jesus’ ability to save him.
Jesus: God so loved the world that He sent Me, so that anyone who believes in Me will have eternal life. I did not come to judge the world, but to save it through Me. If you believe in Me, you will not be judged. If you do not believe in Me, you will be judged. Light has come to this world, but men prefer darkness because their deeds are evil.
Then Jesus goes off to Judea and starts baptizing people. John’s disciples get annoyed that everyone is leaving their master and flocking to Jesus, but John tells them to chill. His ministry is given by God and he was sent to point people to Jesus.
John the Baptist then repeats what Jesus just said about how salvation is about belief in Jesus… which… if he really knew that, you’d think he wouldn’t want any of his disciples to stay with him, but would tell them to all go to Jesus. I think the author might have taken a bit of license and put those words into John’s mouth.