The key to the Apocalypse is to practise it, ie, to make use of it as a book of spiritual exercises composed of twenty-eight exercises. For as the Apocalypse is a revelation put into writing, it is necessary, in order to understand it, to establish in oneself a state of consciousness which is suited to receive revelations.
It is the state of concentration without effort (taught by the first Arcanum), followed by a vigilant inner silence (taught by the second Arcanum), which becomes an inspired activity of imagination and thought, where the conscious self acts together with super-consciousness (teaching of the third Arcanum).
Lastly, the conscious self halts its creative activity and contemplates – in letting pass in review – everything which preceded, with a view to summarising it (practical teaching of the fourth Arcanum).
The mastery of these four psychurgical operations, symbolised by The Magician, The High Priestess, The Empress and The Emperor, is the key to the Apocalypse. One will search in vain for another.
Unknown author, Meditations on the Tarot, Letter IV, The Emperor