“How can a man be born when he is old?” Nicodemus asked. “Surely he cannot enter a second time into his mother’s womb to be born!”
Nicodemus does not understand. The principle Jesus is stating goes against everything Nicodemus has ever been taught. The Jews, by obeying the Law, tried to attain conformity and thus to become, but they could never attain the state of being; Jesus states that a man must be in order to become.