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

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.

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.

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?

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.

3:6 That which is born of the flesh is flesh; and that which is born of the Spirit is spirit.

3:7 Marvel not that I said unto thee, Ye must be born again.

To see the kingdom of God a man must be born again.

The kingdom being spoken of is the prophetic Davidic kingdom on earth, in which Christ will reign along with the believing remnant, the Israel of God (Exodus 19:5-6 Luke 12:32 Psalm 22:28 Galatians 6:16).

To enter into the kingdom a man must be born of water and of the Spirit. Israel had to believe on the name of Jesus; believe he was the Messiah, the Son of God (John 20:31 1 John 5:13). Jesus is saying that Israel had to repent and confess their sins as a nation and be water baptized and receive the Holy Spirit (Acts 2:38).

The Holy Spirit under the fulfillment of the new testament will cleanse Israel with water and put a new spirit in them and cause them to walk in his statutes, keep his judgments, and do them (Ezekiel 36:24-28).

Jesus in saying "Ye must be born again" speaks of the nation of Israel.