John 2:23:  Now when he was in Jerusalem at the passover, in the feast day, many believed in his name, when they saw the miracles which he did.

Remember the law was to come to Jerusalem at passover so Christ is there.  Now notice that many believed, but only when they saw the miracles he did.  Blessed are you who believe and do not see.

John 2:24:  But Jesus did not commit himself unto them, because he knew all men,

This word commit doesn’t quite cut it.  Let’s pull it up.

G4100  πιστεύω  pisteuō  pist-yoo’-o
From G4102; to have faith (in, upon, or with respect to, a person or thing), that is, credit; by implication to entrust (especially one’s spiritual well being to Christ): – believe (-r), commit (to trust), put in trust with.

So it isn’t that Christ didn’t have faith unto himself it means that he knew their faith was because they saw the miracles.  Thus he knew all men and really today if you have that gift of discernment it isn’t that hard for the Holy Spirit to reveal a person’s motives or where their mind is.

John 2:25:  And needed not that any should testify of man: for he knew what was in man.

And this is just a continuation of this thought.  Testify here is bear witness.  Christ didn’t need anyone to tell him what was in the heart of  a man.

John 3:1:  There was a man of the Pharisees, named Nicodemus, a ruler of the Jews:

They are still in Jerusalem.  A a ruler in Jerusalem is a member of the Sanhedrin.  The same Sanhedrin that will eventually demand Christ gets crucified.  Most likely Nicodemus (meaning conqueror of the people) was not there at that time along with Joseph of Arimathea.
History tells us that he was one of the richest men in Jerusalem.  Ever hear of a rich super preacher?

John 3:2:  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.

Note when Nicodemus comes to him.  Does he arrive by day? No he comes at night no doubt to hide his visit from the rest of the super preachers errr I mean Sanhedrin.  I am sure he would be in hot water if Caiaphas heard about this.

I don’t want you to get the wrong picture of Nicodemus.  He does recognize that Christ is sent from God that is a far cry from the rest of them that think he casts out devils in Satan’s name.  And he does call him Rabbi meaning master, it’s a respectful address.

John 3:3:  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.

I am sure you have all heard the phrase, “born again,” but really it means born from above.  Let’s pull up the word.

G509  ἄνωθεν  anōthen  an’-o-then
From G507; from above; by analogy from the first; by implication anew: – from above, again, from the beginning (very first), the top.

John 3:4:  Nicodemus saith unto him, How can a man be born when he is old? can he enter the second time into his mother’s womb, and be born?

Nicodemus isn’t getting it, but don’t worry Christ will explain.

John 3:5:  Jesus answered, Verily, verily, I say unto thee, Except a man be born of water and of the Spirit, he cannot enter into the kingdom of God.

This is why again doesn’t really convey the complete thought.  We are born from water meaning the water in the womb.  What breaks before we come?  And of the spirit.  This is from above and without Christ our spirit is dead.  The wages of sin is death.

John 3:6:  That which is born of the flesh is flesh; and that which is born of the Spirit is spirit.
John 3:7:  Marvel not that I said unto thee, Ye must be born again.

See Christ expects a leader of Israel to know this.

John 3:8:  The wind bloweth where it listeth, and thou hearest the sound thereof, but canst not tell whence it cometh, and whither it goeth: so is every one that is born of the Spirit.

Sometimes I wonder if the translators of this verse fell asleep.  They did a great work, but did they read this and expect anyone to understand it?

the word wind here is pneuma and should be spirit.  Let me try to put this verse in a way you can follow

The Spirit breathes where it He pleases, and you hear the voice thereof, but you cannot tell where is comes from or where it goes:  so is every one that is born of the Spirit.

Basically it says that the Holy Spirit goes where it will, but we can’t tell where it comes from.

John 3:9:  Nicodemus answered and said unto him, How can these things be?
John 3:10:  Jesus answered and said unto him, Art thou a master of Israel, and knowest not these things?

This is the second time that Christ is asking why he doesn’t know.

John 3:11:  Verily, verily, I say unto thee, We speak that we do know, and testify that we have seen; and ye receive not our witness.

Truly, Truly we (him and the disciples) have told you that we know and we tell you this, but your not believing us.

John 3:12:  If I have told you earthly things, and ye believe not, how shall ye believe, if I tell you of heavenly things?

It’s easy here to look down upon Nicodemus here, but how many of us understand the spiritual things Christ teaches?  Do you understand the parables and why he fed the 4,000?