Perhaps you could clarify the idea of “spiritual motion effected by grace”. Even the acquiring of knowledge is a physical process. To learn french from a book for example, there must be a physical interaction with the book. This process involves both a change in the state of the book, and an accompanying change in the state of the person reading the book. It’s not a one way interaction. As far as we can tell, every change is in fact a twofold change, requiring a change in both of the parties involved.
How does a spiritual motion effect change in a physical entity if not by a physical process?
Man is a rational animal, a homo-sapien, meaning a knowing being, a rational being, in short body and soul. Knowledge of soul comes from what the abilities of man are: He can reason, think, choose,and involve all the other things applied to animals, the five senses, local motion etc. The powers of man indicate a source of that power. To think and reason is not a power associated with physical activity such as sensation or physical movement. To abstract the idea (not physical) or concept from sensed objects ( the objective external world) and to use reasoning to acquire new knowledge are not physical activities. What some people do not understand (which is not physical) is that the spiritual soul acts in unison with the physical body, and there is an extrinsic dependence on the body for the operation of the soul through its power of comprehension, and volition. Intelligence(knowing) is one of the operations of the soul, but it can not operate if the brain is damaged seriously because of this extrinsic dependence. The brain is not the intellect, the soul uses the brain to supply it with the sensations of the outer world, and from those impression draws abstraction or ideas about the nature of the outer world. We say soul is spiritual because it is not seen, exists, can not be sensed, but ONLY UNDERSTOOD THROUGH THE RATIONAL POWER OF THE SOUL AND CAN KNOW ITSELF WHICH IS NOT A PHYSICAL ACTION.
Also man demonstrates the ability to choose between two ideas, again, this is not physical, and this ability demonstrates the power of the will, a spiritual faculty belonging to the soul, it is called “volition” This is just a short synopsis of Rational Psychology, one of the studies of scholastic philosophy included in Metaphysics. Psychology literally means the study of the soul, and society translates into "the study of human behavior, it’s effects, the study of the mind, and they reach the mind through the brain, they do not make this distinction, the intellect of man is not the brain. They do not treat the soul,except by introducing into the mind some knowledge of irregular rational behavior such as too much anxiety, but they also affect operation of the mind through the brain eg. by the use of drugs. It does not reduce the inherent ability of the soul to rationalize, but because of the mutual dependence between soul and body it can impede the functions of the mind(intellect). To help you understand just remember, that human actions contain two elements, one spiritual, one physical, and they, in this life, act together, that is the nature of man, body and soul This is clearly demonstrated in the study of the human emotions.
The reading of a book is the ability of first seeing the book, through the senses. The book contains, letters, the combination of which , are assigned meanings, meanings (abstractions or ideas, or concepts of the objective world outside of the mind) and it’s the ability of the intellect, or the mind to understand the relationships of the meaning through the written word (the combination of letters) Again this power is not physical, but depends on the physical brain to supply it sense impression, and sense memory. Metaphysically it is said that the soul is the form of the body, that makes the body what it is, it is the moving power of the body causing all the natural activity of the body.
When it come to the action of divine grace, your are dealing with the moral actions involved in the moral life of man. Grace is the work of the Holy Spirit purifying the moral actions of man, and causing man to grow in moral virtue, eg. Theological virtues of Faith, Hope, and Love. These virtues raise man’s moral, and ethical actions to a supernatural level. They sanctify, make holy the person in his soul, a spiritual entity like God who is Pure Spirit Grace causes this change in the soul of man, and it is purely spiritual. I hope my explanation is sufficient to give you some understanding how even in the spiritual world, there is cause, and effect.