It occupies the first place in the series because if one does not understand it (ie, take hold of it in cognitive and actual practice), one would not know what to do with all the other Arcana.
For it is the Magician who is called to reveal the practical method relating to all the Arcana. He is the “Arcanum of the Arcana”, in the sense that he reveals that which it is necessary to know and to will in order to enter the school of spiritual exercise whose totality comprises the game of Tarot, in orer to be able to derive some benefit therefrom.
In fact, the first and fundamental principle of esotericism (ie, of the way of experience of the reality of the spirit) can be rendered by the formula: Learn at first concentration without effort; transform work into play; make every yoke that you have accepted easy and every burden that you carry light!
This counsel, or command, or even warning, however you wish to take it, is most serious; this is attested by its original source, namely the words of the Master Himself: “My yoke is easy, and my burden is light.” (Matthew, xi, 30)
Meditations on the Tarot, Unknown Author, Letter I, The Magician