A Pharisee named Nicodemus, a ruler of the Jews, goes to Jesus at night and says he knows Jesus has come from God, because no one can do the signs he does unless God is with him. Jesus answers that unless someone is born again he cannot see the kingdom of God. Nicodemus asks how an old man can be born; Jesus clarifies that one must be born of water and the Spirit, and compares the Spirit's work to the wind, which you hear but cannot tell where it comes from or where it goes. Nicodemus asks again how this can be, and Jesus is surprised that a teacher of Israel does not understand. He says he speaks of what he knows and has seen, that the Son of Man came down from heaven, and that just as Moses lifted up the serpent in the wilderness, the Son of Man must be lifted up so that everyone who believes in him may have eternal life.
Verses 16 to 21 explain the purpose. God so loved the world that he gave his only Son, so that everyone who believes in him will not perish but have eternal life. God did not send him to condemn the world but to save it. Whoever believes is not condemned, but whoever does not believe is already condemned, because the light has come into the world and people loved darkness more. Whoever does the truth comes to the light.
Afterward Jesus goes with his disciples into the land of Judea and baptizes there, while John the Baptist is baptizing at Aenon near Salim because there was much water. A discussion about purification arises, and John's disciples tell him that everyone is now going to Jesus. John answers humbly: he is not the Christ but the friend of the bridegroom, who rejoices at the bridegroom's voice, and Jesus must increase while he decreases. The chapter closes with a word about the Son, sent by the Father: whoever believes in him has eternal life, and whoever rejects the Son will not see life, and the wrath of God remains on him.