There are of course many more questions left unanswered by Science than the number it is able to answer. Here are a few of them — some old, some recent: What is life and where and how does it originate? We do not know. What is electricity? We do not know. What determines sex? We do not know.
Very well, then. The answers to these questions are — for Science — mysteries. But, as the answers must exist, they remain for Science occult or hidden knowledge. Some day (perhaps) Science may find those answers. Then such knowledge will pass from the occult into the field of the known. It will no longer be a "mystery."
In a Mystery-School the situation is reversed. The answers to all the at present unanswerable questions are well known. They make up, so to speak, the curriculum of a Mystery-School. The teaching of such answers to carefully selected pupils, and the eventual initiation of these pupils into wider fields of knowledge was covered by the ancient terms "Mystery-Teaching" and "Mystery-School." And they were called "Mysteries" because for the general public that was exactly what they were. It is of course self-evident to a Theosophist that there must be such schools or their equivalents in every range of being; for the only individual in our Universe for whom there are no longer any mysteries is the Cosmic Hierarch.
Another point — one of such breath-taking urgency at the present time — the terrible misuse of the advance in our knowledge for progressive world-destruction. The only solution for this situation is the reappearance of the Mystery-School as a vital factor in shaping our civilization. Consider one of the basic axioms of this ancient institution — Discipline precedes the Mysteries. There you have it, the remedy for the grisly suspense that hangs over us. A Mystery-School where the right discipline along ethical lines of self-mastery is given before any man is allowed to have knowledge of vital import to the safety of others. As it is, knowledge of any and every kind is now broadcast so that it can be used not only by good men but by any fiend who cares to appropriate it for the gratification of his appetites.
This carelessness in the safeguarding of creative knowledge is one of the most tragic failures of what we call modern civilization. We have appropriated the secrets of Nature — rifled her storehouses without first having paid the legitimate price in self-discipline. And already we are making forced payments on the account. Later, if we do not soon mend our ways, there will be compounded and pyramiding interest to be met. How? Perhaps in a similar way to that we learn of in The Secret Doctrine, by which the Atlanteans expiated their crimes against Nature. So that the anthropologists and palaeontologists of future ages may uncover but dim dust-heaps of what are now magnificent cities; may find the "Stone-Age Man" of the future roaming the once more engulfing forests — degenerate men whose ancestors were our moderns and progressives — savages in whom submerged memories may inspire to pottery and metal-smelting and weaving, with other "primitive" cultural and economic activities.
Can this happen? Why not? Time never stops turning its slow inevitable wheel. What has been is but too likely again to be. The marvelous rock-drawings of Altamira were the resurgence of such submerged memories in the souls of degenerate remnants of prehistoric Atlantis.
Is it any wonder that H. P. B. with the Masters behind her bent a great part of the energies of her last years in laying the foundations for a Mystery-School to rescue our civilization?