Nicodemus comes to the Savior in the middle of the night (bad smoke alarms?) and asks Jesus questions he should have known the answer to. The Savior in verse 10 asks him why he isn't teaching these things if he has the writings of the prophets and is a Rabbi? The Jews must have been almost devoid of using the scriptures and only discusses things related to keeping the Law of Moses.
Verse 23 is another proof that baptism was done by complete immersion. Why go all the way to Aenon, where there are lots of springs and pools of water to simply sprinkle? The word baptism comes from the Greek word Baptizo which means to make fully wet or fully immersed. In Romans and Colossians the words "buried with him in baptism" are used. Immersion is important because being completely immersed in our baptism symbolizes the Savior being buried in the tomb and then coming up out of the water symbolizes his coming forth out of the tomb a newly resurrected being to live eternal life. We come up out of the water a new person, washed clean and ready for a new spiritual life.
John says that he must begin to decrease his ministry as the Savior increases his. I wonder if John also had an inkling that his life would be short.