The whole card seems to be a little alchemical discourse.
The wheel revolves, reminding me that the whole basis of the alchemical process is about circulation.
In needs to be performed in an 'arena' or environment of balanced elemental forces. (One can even equate the lab and apparatus to the elemental formula much as a blacksmiths; workshop fire water air earth : forge quenching bellows anvil.
Within are the three elements ... yes there are 4 sorta ... a primary element that contains the 3, from which they are divided and a 4th when they are bought back together.
Another 3:4
The Gunas - This Vedic principle is an example of the primary triangle. In Samkhya philosophy, there are three major Gunas that serve as the fundamental operating principles or 'tendencies' of prakṛti (universal nature) which are called: sattva guṇa, rajas guṇa, and tamas guṇa. The three primary Gunas are generally accepted to be associated with creation (rajas), preservation (sattva), and destruction (tamas).
Beyond these forces or their influence or balanced within them lies a ‘supernal consciousness, depending on the tradition; Brahma, Krishna, etc. “The World deluded by these Three Gunas does not know Me: Who is beyond these Gunas and imperishable.” Who is this ‘Me’?
Here we have another three implying a fourth, this time , ‘above’ (as opposed to ‘below’, a pendant or result, i.e. 4, balance all three above or bring into manifestation, bring together back to a unity that has grown from the process of splitting the one into two / three).
A good example is the dialogue from the first part of The Rite of Jupiter . There are three central characters representing the Gunas and a central character; Centrum in Centri Trigono (C.I.C.T.) – the one in the centre of the triangle. But here Crowley, although identifying them with the gunas lists them as feeling thought and ecstasy.
Later in the play, the ‘Gunas’ argue, C.I.C.T. admonished them;
C.I.C.T. “Irreconcilable, my children, how shall ye partake of the Banquet of Jupiter, or come to the centre of the wheel? For this is the secret of Jupiter, that He who created you is in each of you, yet apart from all; before Him ye are equal, revolving in Time and in Space; but he is unmoved and within.”
Although it appears as a map of three it is describing a process of four (or 3 ‘implies’ 4). One example is a three sided pyramid that creates an apex or a three sided pyramid and its base. Models of three often include a fourth principle (originating) above or within the triangle (the eye within the triangle symbol) or extending ‘below’ to show an ‘outcome’, e.g. all three elements combine to make earth.
The three model with the 'One' resultant (instead of concealed within) - making the 4 model is everywhere present:
The 4 world of the Qabalah, Tarot suits and elements, G A C T - genetic code, divisions of the soul (and many other things) in Kabbalah, the four systems of the body ( nervous, circulatory respiratory, muscles skeleton, etc ) - note the fire water air earth arrangement in this and the other examples), the four Buddhist principles for divine living : Loving kindness, Compassion, Equanimity (balanced mind) and Appreciative Joy (or Sympathetic Joy) - and the 'Four Noble Truths' , four principles of Aikido, 4 male archetypes ( King, Warrior, Magician, Lover), the 3 'emergency drives' of Psychology (the 4th being the actual physical response (earth) to the drives, the Three Psychic Divisions of Freud and the Fourth Jung added, vegetative life ( A plant needs four elements plus the ‘fifth element’ to grow ('quintessence is seen as 'hidden' in the elements or a pre sate that generated the elements); ‘Spirit’– light. Fire – temperature. Water – moisture. Air – CO2 and O2. Earth – ‘growing medium’. Most consist of 4 basic components; seed (archetypal pattern)and fruit (or seed container), flowers (or their equivalent), leaves / stems and roots ( also ; Primary nutrients for good plant growth; N, P & K. Further to this we can construct another triangle of nutrients with N, P & K at one point, secondary nutrients at another ( Ca, S & Mg) and micro-nutrients ( B, Cl, Mn, Fe, Zn, Cu, Mo & Se) at the third - fertiliser should be put out with lime to maintain Ph balance, so that is the 4th grounding principle) ... also ; Four principles for agricultural consideration; cosmic forces, earthly forces, location and type of plant. The Four Forces in Physics. Four psychological truths ( review the internal map, witholding truth, sublimation of desire and balancing the first three - a great demo of the 4th coming from the 3rd).
Colour perception is a good demonstration; singularity splits into duality, the main pattern is a reception of 3 but that creates 4 and result : There are 3 ‘primary’ colours; red, blue, yellow. There are 4 ‘natural’ colours; red, blue, yellow green : fire, water, air, earth.
We look at one thing ... through 2 eyes. We have 3 sets of colour receptors; black and white, blue and yellow and red and green. These three combine to give hundreds of possible hues like purple and magenta.
Within the eye the retina has two types of light sensitive cells called rods and cones. Cones absorb red blue and yellow but do not work well in detecting colour in low light. Rods have ‘sacrificed’ colour reception to work as ‘night vision’ and detect black and white.
Signals travel from the retina along the optic nerves to the visual cortex for sorting and sending to the three relevant parts of the brain to analyse the signals in respect to three qualities; movement, colour, distance. These three parts of the brain send their processed information back to the visual cortex where it integrates the information.
Light – singularity, passes through two types of receptors to make three dimensions of colour, in a duality (or polarity) black / white, blue / yellow, red green, to process through the visual cortex to three parts of the brain and back again to make it possible to observe the four ‘natural colours’ and their combinations.
So, in my view the revolving wheel with 3 characters on it, amidst the world generating 4 principles is an underlying principle of order and structure in nature.