Jesus Said You Must Be Born Again

“Truly, truly, I say to you, unless one is born again he cannot see the kingdom of God.”
Nicodemus said to him, “How can a man be born when he is old? Can he enter a second time into his mother's womb and be born?”
Jesus answered, “Truly, truly, I say to you, unless one is born of water and the Spirit, he cannot enter the kingdom of God.
That which is born of the flesh is flesh, and that which is born of the Spirit is spirit.
Do not marvel that I said to you, ‘You must be born again.’
The wind blows where it wishes, and you hear its sound, but you do not know where it comes from or where it goes. So it is with everyone who is born of the Spirit.”

When Jesus spoke of "water" and "spirit", there is only one Old Testament passage that this could refer to.  When Nicodemus does not understand this, he gets this response:

Nicodemus said to him, “How can these things be?” Jesus answered him, “Are you the teacher of Israel and yet you do not understand these things?”

Here is the passage in Ezekiel chapter 36 that Jesus was referring to:

I will sprinkle clean water on you, and you shall be clean from all your uncleannesses,
and from all your idols I will cleanse you.
And I will give you a new heart, and a new spirit I will put within you.
And I will remove the heart of stone from your flesh and give you a heart of flesh.
And I will put my Spirit within you, and cause you to walk in my statutes and be careful to obey my rules.
--Ezekiel 36:25-27