Summary: Jesus shares with Nicodemus the need to be born again as the basis for righteousness, spirtual perception, and eternal life.
VERSES 1-2 A Visit at night
Nicodemus approaches Jesus by night. We need to remember that in the days before electricity people did not usually run around at night. There are only two assumptions we can make about Nicodemus visiting Christ at night and both of them are reasonable. First, that at night Jesus was not occupied with ministry concerns and therefore surrounded by people and Nicodemus could obtain an audience with him. Second, that Nicodemus did not want the people to see him, a representative of the Jewish ruling council, approaching Jesus. Both are probably correct.
His approach is, on the surface, respectful. He speaks for a group. There is often a discussion of whether he was speaking for the Jewish Ruling Council or for a schism of this group that also included Joseph of Arimathea who provided for the burial of Christ in the garden tomb. It is my opinion that the very fact that John mentions the ruling council is indicative that Nicodemus has come as their representative.
Nicodemus declares that those he represents know by the signs and wonders that Jesus has come from God. That is almost comical when you consider that we read in multiple places that these very same people deny Jesus publicly about the basis of his authority for teaching, healing, etc. In John 9, the Pharisees disagree that Christ came from God because he healed a man born blind on the Sabbath. In Luke 20 the Chief Priests and teachers of the Law and approach and demand to know by what authority he was ministering under. Absurd! They had already sent Nicodemus with a declaration that they knew he came from God, but then again, perhaps they were offering simple lip service and did not believe that at all.
VERSES 3-8 The Need to be born again
Jesus did not waste any time with the flattery offered by Nicodemus. Instead he told Nicodemus that he (and the Jewish Council) lacked spiritual perception because they needed to be born again. Jesus was pointing out in a clear and undeniable manner that if Nicodemus and the ruling council wanted spiritual perception then there would have to be an experience that was a start over from square one.
Nicodemus was confused by the analogy that Christ offered him. How could an old man be born again? Jesus said that there are two births, one by water and one by blood. Some interpret the reference to water birth as a necessity for baptism. I don't see that here. I believe it is a clear reference to the natural birth, as a child is suspended in an amniotic fluid (water) for nine months and then born in a gush of fluid after the mother's water breaks. He is telling Nicodemus that a spiritual birth is necessary.
Jesus did not even give them credit for their religious zeal, their fervor for the Law, or their observance of religious ritual. It is not religious practices that redeem people and provide spiritual insight, it is a born again experience with God.
Paul spoke about this issue in Philippians chapter three. A group of false teachers wanted to add religious works to faith in Christ as a path to salvation. Paul wrote about those people using some opposites. (See Philippians 2 verse 3) He told the people to watch for them and used three very nasty names for them. He called them dogs, evildoers, and mutilators of the flesh.