Hey, John looks like a great topic!
For starters, let's look at some context.
John 3:9 (NIV) “How can this be?” Nicodemus asked.
10 “You are Israel’s teacher,” said Jesus, “and do you not understand these things?
We first notice that Nicodemus is a teacher, which means he has the entire Bible memorized. Not only that, but he is versed in all of the "commentary" which means he's a pretty smart guy. It also means that somewhere there is a commentary on one or more of the passages, probably within Torah ( first five books of the Bible) that speaks to being born again.
For starters, John uses a Jewish writing style called first mention. When we see a keyword being used in Johns writing, it's almost safe to always go back to the first place in the Bible that word is being used.
Let's look at John 3:16 (NIV) For God so loved the world that he gave his one and only Son, that whoever believes in him shall not perish but have eternal life.
Love, it's found in Genesis 2:2 Then God said, “Take your son, your only son, whom you love—Isaac—and go to the region of Moriah. Sacrifice him there as a burnt offering on a mountain I will show you.”
Moriah is where the temple is built in Jerusalem and is said to be where Adam was formed, Jesus being the second Adam.
Without going into great detail, the story in Genesis parallels that off. Jesus.
The writer of Hebrews put it this way, and of course, this has everything to do with faith.
Hebrews 11:17 (NIV)
By faith Abraham, when he was tried, offered up Isaac: and he that had received the promises offered up his only begotten son,
18 Of whom it was said, That in Isaac shall thy seed be called:
19 Accounting that God was able to raise him up, even from the dead; from whence also he received him in a figure.
Verse 19 is oral tradition aka commentary... Commentary Nicodemus obviously had either dismissed or wasn't taught.
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