A wheel within a wheel is the machinery of the head seen from inside, the turning chambers and rings of the brain that the prophet renders as revolving structures of light. This is anatomy hidden in vision, the cranial works described as wheels because that is how the inner apparatus appears to the one who beholds it.
The 4 sharing one likeness are the 4 stages of consciousness, the levels a person passes through set turning as a single works. The brain is a biological machine that waits for an operator, and here it is drawn as gears of light, the equipment through which awareness moves once someone learns to run it.
The wheels: the turning chambers and rings of the brain, the head's inner machinery seen as revolving light
Beryl: the clear luminous color of that inner apparatus when it is beheld within
The number 4: the 4 stages of consciousness a person moves through, here set turning as one works