John 3:1-3

John 3:1-3. 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.

There must be a new birth because a new name is absolutely necessary for the discernment of spiritual things. The natural man cannot comprehend spiritual things, they must be spiritually discerned. The new birth is therefore necessary that we may have a spirit within us which can see or understand the kingdom of God; but until a man is born again, "he cannot see the kingdom of God."