When Jesus told Nicodemos that he had to be born again ,it was to let him know that he could not know the things of God until he was born again. Nicodemos could only think of one way that a man could be born again,and so did all the others that Jesus had not revealed the answer to. In a carnal state of mind, going back into a person's mother's womb would be the logical and impossible way. He knew it had never been done before, and wondered if Jesus could do it. God's plan was to not give rebirth to the flesh which would have required everyone going back into their mother's womb, and also would have been a backwards process. God don't go backwards or reverse anything he do. On the other hand, a man could be reborn in the spirit, that spirit man that lives in the body. It can be renewed, cleansed, and fresh to start over the same way a natural born baby is born in the flesh .Anew spirit is born to be taught by the Holy Spirit that a person must have to be renewed. Same old body, but a new spirit., and it will teach you only of heavenly things from above,and nothing of this world. This is when all your pass sins have been washed away, Jesus said all things are new from that point on. You will have become a new creature, but this time in Jesus Christ, instead of the world. So now that the spirit of holiness is in us, it gives life to the spirit, and because of that life, our flesh is dead and sin in it has been condemned. When light takes over darkness, darkness is rendered helpless.