Something that is difficult or impossible to understand or explain.
"As a subject which does not admit of verification by the prescribed canons of mechanical physics is held to be unworthy of attention, as untenable, it is fortunate for the cause of humanity that modern science has reached its ultima thule, where the tide of materialism must set back and carry with it the drift-wood of skepticism which has been accumulating during this century.
To quote the words of a physicist (at the Forest Gate Physical and Chemical Laboratories), "The door, between us and the spirit-world, which it has been declared is shut and bolted is even now ajar and a few gleams of light are struggling over the threshold from Keely's discoveries."
The artificial beacon, fed with the oil of learning, so proudly held aloft by modern science, is flickering; and many great minds are rebelling against the darkness in which it has plunged the mysteries it sought in vain to unravel. The Popery of scientific authority must have its downfall now that researchers after knowledge are making a stand and contending their right to think for themselves, instead of allowing dogmatic science to decide for them.
There is a light which sympathetic physics teaches us will never fail: - the inner light, or intuition, if we seek its guiding rays. The Spirit of Truth will lead us into all truth is the promise given by One who spake as never man spake before; and, with the foundation stones of pseudo science crumbling away, there is nothing left to fall back upon but the fortress of Revelation." [Veil Withdrawn]
 To give a greater understanding of events at Sais, that ancient Egyptian city in the Nile delta, The Secret Doctrine by H P Blavatsky relates: "...And how little Herodotus could tell is confessed by himself when speaking of a mysterious tomb of an Initiate at Sais, in the sacred precinct of Minerva. There, he says 'behind the chapel is the tomb of One, whose name I consider it impious to divulge... In the enclosure there are large obelisks and there is a lake near, surrounded with a stone wall in a circle. In this lake they perform, by night, that person's adventures, which they call mysteries. It is well to know that no secret was so well-preserved and so sacred with the ancients as that of their cycles and computations. From the Egyptians down to the Jews it was held as the highest sin to divulge anything pertaining to the correct measure of time. It was for divulging the secrets of the Gods, that Tantalus was plunged into the infernal regions; the keepers of the sacred Sybilline Books were threatened with the death penalty for revealing a word of them.' The Secret Doctrine, Vol II, page 396. While not directly related to the Seven Veils of Sais, the following quotation from The Secret Doctrine, Vol. III, p.132, may afford further insight into what was hidden behind them. "An impenetrable veil of secrecy was thrown over the Occult and Religious Mysteries, after the submersion of the last remnant of the Atlantean Race, some 12,000 years ago, lest they should be shared by the unworthy, and so desecrated. Of these Sciences several have now become exoteric — such as astronomy, for instance, in its purely mathematical and physical aspect." Ed. [The Energy Evolution - Harnessing Free Energy from Nature, The Life-Current in Air and Water]
Science was once the prerogative of the few. It was transmitted only under the seal of secrecy, to chosen men from whom rare moral qualities were required. These chosen ones were placed in the presence of emblems and symbols, because language primitively lacked terms to express abstract things. It was therefore necessary to cover the philosophical conceptions with a colorful veil, which had to be transparent for the discerning minds. Science is only addressed to elite intelligences.
To acquire the knowledge specific to the ancient sages, it was not enough to exercise memory and bring into play a certain ease of assimilation. There was a time when you only learned by solving puzzles. The truths that were thus discovered had nothing in common with the usual knowledge that we seek so widely to spread today. — The Wisdom of the Ancients attached itself to the highest speculations: it sought the causes and especially the Cause of the causes. — Modern science, on the contrary, studies effects: it observes and it calculates; but too often she dispenses with thinking. — Antiquity tended to produce sages, whereas today we only have scholars.
The very legitimate triumph of experimentalism must not, however, cause us to lose sight of the order of those truths which are within us and not outside of us, — Thought is subject to laws, the knowledge of which alone can enable us to distinguish reality from appearance in all things. The man who ignores these laws is the plaything of perpetual illusions, because he knows neither how to control nor to rectify the data of his senses.
The thinker, on the contrary, who is initiated into the Mysteries of Being, conceives the necessary conditions of all existence and cannot be fooled by any misleading mirage. When one has known how to conquer this initiation, one ceases to agitate blindly within the darkness of the profane world, one lights up with a torch that dissipates the darkness that one carries within oneself, one holds the thread of Ariadne which allows one to penetrate without getting lost in the labyrinth of misunderstood things." [Oswald Wirth]