Read: John 3:1-15
Do not marvel that I said to you, "You must be born again." (John 3:7 ESV)
Nicodemus, himself a religious leader of the Jews, came in secret to Jesus to confess his acknowledgement of Jesus as a messenger and teacher sent from God. He didn't acknowledge Jesus as the Christ, only as a miracle worker who clearly had the blessing of God upon his ministry. Jesus responded with a teaching that has become a permanent part of traditional Christian vernacular. He told the Pharisee that he could not be part of God's kingdom unless he was "born again."
This was a new idea to Nicodemus and he confused Christ's meaning with one of earthy implications. Jesus' frustration with Nicodemus' lack of understanding was apparent. How could someone who professed to be a follower of God and a teacher of the Law so easily confuse or misunderstand the path to God?
I don't know what you're background is. I don't know your religious history. All I know is that like the Pharisee did we need to humbly approach Jesus and seek answers. In terms of rebirth we need to submit ourselves to the kind of spiritual rebirth that can only be experienced through the supernatural miracle of salvation. We all must be born again.