"Now of the process of re-birth there is and always has been a definite and exact science, the knowledge of which has been the property of the smallest of minorities and, for adequate reasons, has not been suffered to be promulgated to the multitude, although individuals who earnestly sought for it never failed in discovering it.
The Mystery-schools of antiquity, at least before the days of their degeneracy, possessed and administered it; it was the raison d'etre of their existence, as was well known to the public
of the time, any member of whom, prepared to abandon secular life and apply himself to the higher vocation, could seek admission therein. The Christianity of the first two centuries took over the doctrine and the science, confirmed and expanded as they became by the advent of Christ, but eventually lost them and put in their place the ecclesiastical machinery and dogmatic theology which have ruled throughout the subsequent centuries of European history, with the result that popular Christianity has for long known nothing of them. With the enjoinder of the assured necessity for regeneration proclaimed by the Master of their faith it and its theologians and pastors are well familiar. But can it be said that 'Ye must be born again' means for them more than a vague, mysterious, metaphoric counsel of perfection capable of being satisfied by living the ordinary natural life as far as possible in accordance with the standard of conduct indicated in the Gospels? Are the words accorded more than a value for ethical purposes, to the total neglect of the possibility of their literal practical fulfilment?"
Walter Leslie Wilmhurst, Introduction to M. A. Atwood,
Hermetic Philosophy and Alchemy