I have studied astrology, and that gave me an advantage when reading a few sections of the Bible. I've also discussed astrology with an Orthodox Jew, and we agreed on how it can be used both unlawfully and lawfully.
Take the four cherubim for example. Someone who's studied astrology sees something almost immediately when a lion, a calf, a man and an eagle are mentioned. Another example is the order of the metals here:
Numbers 31:22 Only the gold, and the silver, the brass, the iron, the tin, and the lead,
Mercury or quicksilver is missing since it wasn't known to them; but the rest are lined up according to how astrologers line up the planets which rule metals: Sun, moon, Venus, Mars, Jupiter, and Saturn.
Counting the value of letters (gematria) is also a magical thing straight out of kaballah. Then there is the matter of the cherubim I mentioned above.
The Jews who had the highest level of understanding in this hidden knowledge never discussed it openly. It was passed on orally. They may hint at it however. Paul obviously had some knowledge of it -- you can see that in his writings at times, and he studied with Gamaliel. John certainly had studied it.
To Nicodemus now. The conversation starts off strangely. You noticed the odd break, but didn't investigate it enough. Nicodemus appears to pay Jesus a high compliment and Jesus appears to ignore it and start talking about something else entirely. What was going on? No learned rabbi would say what Nicodemus said and be sincere about it. Nicodemus is fishing because he's not sure who or what Jesus is. "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." That makes no sense for anyone who knew what Moses said. Signs and wonders do not prove someone is from God. Moses warned about it. Jesus also disapproved of people craving signs and wonders.
I think Nicodemus was testing Jesus, to see if he was full of pride. He threw out this piece of flattery to see how Jesus would respond. A proud person can be manipulated if you flatter him; so if Jesus showed he could be manipulated, Nicodemus would have known he was not from God.
Jesus did not respond to it He ignored it and began to answer Nicodemus' real but unspoken question. His comment about the "Son of Man" showed Nicodemus he knew something, a little at least. (Why was Ezekiel called "Son of Man"? The Sanhedrin had wanted to round up all copies of the book of Ezekiel and hide them away since the book contained material they preferred the public not have; but it was too popular so they could not suppress it.)
Nicodemus continues playing dumb. "How can a man be born when he is old? can he enter the second time into his mother's womb, and be born?" Some may think that was a sincere question; but I warn people against pride themselves if they are too confident they know things Nicodemus didn't. Jesus says more, and Nicodemus keeps pretending not to know what Jesus is talking about. "How can these things be?" Then Jesus cuts through Nicodemus' act and says, " Art thou a master of Israel, and knowest not these things?" In other words, "Stop pretending not to know what I'm talking about. I know what I'm talking about and you know." You see if Jesus didn't know what he was talking about, Nicodemus wouldn't have wanted to talk about it since the cherubim were talked about only by a few among themselves.
It's tempting to want to believe we today know more than Nicodemus did; but do we? Why did Jesus expect Nicodemus to know these things? Jesus then says that he knows what he's talking because he's seen them. Compare if you will to Ezekiel's experiences of being "caught up" and travelling through the air. Most Christians ignore the part in the Gospel of John that says those born of the Spirit can travel like the wind. They do not connect the dots with Ezekiel who was called Son of Man and who could travel so.
Jesus also goes on to mention the serpent and its significance. To most Christians this remains another mystery. Why would Jesus compare himself to a serpent being raised up? It's clearly connected to the reversal of the serpent being cast down in Genesis; but the question Christians need to ask themselves is how and why should the serpent be raised up?
The conversation between Nicodemus and Jesus ends abruptly. We are not told what Nicodemus had to say; but we learn later that Nicodemus defended him (John 7:50-51) and help bury Jesus (John 19:39-40). That tells me Nicodemus understood what Jesus told him that night and was convinced by it that Jesus was Messiah.
The conversation may seem strange to some, but I do think Nicodemus understood it. The passage becomes obscure if someone believes he already knows what born of the Spirit means before reading the passage and he also assumes Nicodemus couldn't have known. There were some Jewish leaders who knew how to enter the kingdom but refused according to Jesus. They also hid that information, preventing others from entering.
Matthew 23:13 But woe unto you, scribes and Pharisees, hypocrites! for ye shut up the kingdom of heaven against men: for ye neither go in yourselves, neither suffer ye them that are entering to go in.
Typical Christian theology cannot explain that verse since many Christians do not think any of the Jews could know such things.