In 1906, Rudolf Steiner was a well known public speaker throughout Europe. He traveled extensively to give lectures including: An Esoteric Cosmology (Paris), Popular Occultism (Leipzig), The Gospel of St. John and Theosophy Based on the Gospel of John (Berlin). Unfortunately, the notes of three lectures on the Gospel of John given in February and March in Berlin were quite scanty, yet contained essential material concerning Christology. In view of the fact that the publication of Volume 94 in which they were later contained did not occur until 1979, these three lectures were meanwhile printed in typewritten form. The following is from March 5, 1906 in which he discusses initiation and the esoteric meaning of the Transfiguration.
"I would also like to draw your attention to the conversation with Nicodemus, which you will find in the third chapter. There we have the significant words, “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.” What does it mean to be born anew and to see the Kingdom of God? It means to have awakened the higher self, to be born so that the eternal core of one's being is awakened. What does it mean to enter the kingdom of heaven? It means to see not only the reflection of Devachan here on earth as we see it through our physical eyes, but to see this realm directly itself. He alone can do this who has not only been born for this physical world, but is born a second time.
Take what I have used as a comparison, but one which is more than a comparison. Take it literally. To be born means to proceed from an embryo to a stage at which one perceives the outer world with the senses. If one does not pass through an embryonic stage one can never be ready to be born. Those who know this stage also know that ordinary life is an embryonic stage for the higher life. This leads us deep into the meaning of ordinary life. It could be quite easy for someone who directs his gaze towards the spiritual world to become convinced that there is such a world and that man is a citizen of it. He could then proceed to disregard the physical world and to believe that one cannot depart from it quickly enough, and that one should mortify the flesh, the sooner to reach the spiritual world. This shows ignorance. It is as senseless as if one would not allow the human embryo to mature but would bring it into the world at two months, and expect it to live there. Likewise for the higher world, one has to develop to become mature. Such is he who has developed his higher self. The physical world is the school. He who has developed his ego here is ready to enter the kingdom of heaven, which means to be born again. Man has to go through birth and death ever and again, until he has gained his full maturity in order to enter the spiritual world itself, so that he no longer needs physical organs. Thus we have to realise that everything we do by means of our eyes, ears and other senses is work done for the higher life."
Read more: Rudolf Steiner, The Gospel of St. John, Lecture 3, GA 94, 5 March 1906, Berlin.