These figures are also part of the vision of Ezekiel and have lots of significance in Kabalistic/Judaic Merkabah Mysticism. Also the figures of the key have been represented as the fixed positions of the zodiac.
However when we contemplate the symbols in a Gnostic way they represent the Quaternary of Jungian depth psychology. These portions of the personality are represented by air/intuition , water/feelings , earth/sensation and fire/thinking, as each of these elements are represented archetypally it is necessary , for me at least, to take the correspondences into consideration. In alchemy the matter earth is worked upon by the air,fire,water of the alchemical correlations of prima materia, salt, sulphur and mercury. These principals work on the prima materia of the human centers of consciousness more commonly known as the Hindu system of Chakras and energy connections between them. As the middle channel is ascended the prana or breath force is risen through the chakra system activating higher and higher levels of consciousness and resulting in a Gnosis. This process is highly technical, esoteric and dangerous , therefore the experience needs to be accompanied by a Kundalini master.
In our western system however the same Gnosis may be produced by a traversing, traveling a previously traveled route, the path of creation to its “root”. As we make the journey the beginning is in the Arcanum of the XXI key. As we start the ‘yogic path of the west’ we are going to refine more and more our conscious awareness of the transcendental nature of the Fullness and integrate the elements of the personality with the insight of our higher Self.
In Light and Love.