How do you interpret this Bible verse?

"There was a man of the Pharisees, named Nicodemus, a ruler of the Jews: 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. 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. 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? 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. That which is born of the flesh is flesh; and that which is born of the Spirit is spirit. MARVEL NOT THAT I'VE SAID UNTO THEE, YE MUST BE BORN AGAIN" (John 3:1-7).