Major Arcana · Key 21
The World
Read to know yourself, not to surrender yourself: relate to the card; never obey it. These are what two traditions wrote, not predictions.
In Waite's words: The Pictorial Key to the Tarot (1911)
As this final message of the Major Trumps is unchanged— and indeed unchangeable— in respect of its design, it has been partly described already regarding its deeper sense. It represents also the perfection and end of the Cosmos, the secret which is within it, the rapture of the universe when it understands itself in God. It is further the state of the soul in the consciousness of Divine Vision, reflected from the self-knowing spirit. But these meanings are without prejudice to that which I have said concerning it on the material side.
It has more than one message on the macrocosmic side and is, for example, the state of the restored world when the law of manifestation shall have been carried to the highest degree of natural perfection. But it is perhaps more especially a story of the past, referring to that day when all was declared to be good, when the morning stars sang together and all the Sons of God shouted for joy. One of the worst explanations concerning it is that the figure symbolizes the Magus when he has reached the highest degree of initiation; another account says that it represents the absolute, which is ridiculous. The figure has been said to stand for Truth, which is, however, more properly allocated to the seventeenth card. Lastly, it has been called the Crown of the Magi.
The upright and reversed meanings above are from Waite's own list of the trumps' divinatory meanings, Part III §3 of the same book; see them all, with his Celtic Cross, on Tarot spreads.
A. E. Waite, The Pictorial Key to the Tarot (London: William Rider & Son, 1911), public domain.
In the Golden Dawn's Book T (1912)
The Great One of the Night of Time
The matter itself. Synthesis, world, kingdom. Usually denotes actual subject of question, and therefore depends entirely on accompanying cards.
Correspondences
Hebrew letter: ת (Tau, 'cross') — path 32 on the Tree of Life.
On the Tree: path 32 joins Yesod and Malkuth · see it on the map
Attribution: Saturn.
(Classical Golden Dawn / Book T attribution. Modern decks add an outer planet — Uranus, Neptune, or Pluto — to the three elemental trumps.)
Astrological attribution (Book T)
Book T as printed in The Equinox I(8), 1912, public domain (notes in square brackets are Crowley's). The correspondences are this site's compilation from Book T. Open it in the Golden Dawn deck.