John 3:1-3 — There was a man of the Pharisees, named Nicodemus, a ruler of the Jews:
The same came to Jesus by night, and said unto Him, Rabbi, we know that Thou art a teacher come from God: for no man can do these miracles that Thou doest, except God be with him.
Jesus answered and said unto him, Verily, verily, I say unto thee, Except a man be born again, he cannot see the kingdom of God.
These verses are connected to John 2:23-25. Nicodemus was one who saw Jesus' miracles. It seems he sought more truth, but he was afraid for his reputation. He snuck in after dark. Nevertheless among the chief rulers also many believed on him; but because of the Pharisees they did not confess him, lest they should be put out of the synagogue (John 12:42).
In Talmudical literature, Nicodemus Ben Gorian was considered an outstanding figure in Jewish culture.
Ruler of the Jews — probably a member of the Sanhedrin
Rabbi = master, teacher
Nicodemus probably suspected that Jesus was the Messiah, which led him to wonder about the Kingdom. Jesus anticipated this and answered the question before it was asked.
Kingdom — not salvation, as often assumed, but the literal Kingdom which the prophets predicted, promised to Israel and yet to come at Christ's second coming (Ezekiel 36:4-28). But it is also true of us by application — Who hath delivered us from the power of darkness, and hath translated us into the kingdom of His dear Son (Colossians 1:13).
Night could also symbolize Nicodemus's spiritual ignorance. The Jews, like Nicodemus, were in the dark without spiritual discernment and were dead in sin.
Nicodemus was as "good" as a man could be, but the Lord emphasized his need for a new birth.
Men are dead in sin. Birth is the gateway to life.
Born again = born from above
Evidently, Nicodemus believed. Here he is timid, approaching by night. In John 7:50-51, he boldly reprimands the Sanhedrin, and in John 19:39, he boldly helped Joseph of Arimathea bury Jesus when the apostles fled.