'Objection 2
Further, there ought not to be any deception in a sacrament of truth. But we judge of substance by accidents. It seems, then, that human judgment is deceived, if, while the accidents remain, the substance of the bread does not. Consequently this is unbecoming to this sacrament.

Reply to Objection 2
There is no deception in this sacrament; for the accidents which are discerned by the senses are truly present. But the intellect, whose proper object is substance as is said in De Anima iii, is preserved by faith from deception. And this serves as answer to the third argument; because faith is not contrary to the senses, but concerns things to which sense does not reach.'
Thomas Aquinas - Discourses c1270

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Thomas Aquinas' reply has been used in many of the larger images, sometimes perhaps more than a thousand times. It is always hand-written. It is a litany. In some ways it might be heard as a Gregorian chant or the drone on a set of bagpipes.
It proves itself by its repetition.

Some clues towards interpretation:
Deception - You are not deceived; I have not lied
Sacrament - Image; performance; ritual
Accident - that which is left behind; debris; unintended event; apparent random element
Senses - all seven
Intellect - the educated mind
Substance - the material world
Faith - that which you choose to believe