As the vital force is spiritual, it can only be disturbed by some other spiritual force which is inimical to it. This inimical force affects the vital force when the former (inimical force) is superior to the latter (vital force). Because of this affection, the vital force no longer rules with unbounded away. Its normal workings are altered abnormally and the essential harmony is disturbed. This lack of harmony both on sensational and functional plane immediately shows itself through the material body as signs and symptoms. Hence when harmonious functioning of the vital force is disturbed, we get sickness as as result.
... Each one possesses a special personality and a special psychophysical construction which is determined by the interplay of hereditary tendencies and factors of disease.
...The appearance of these disturbances is a reflection of the inward turmoil and confusion of the harmonious action which the vital force has suffered. This brings us to the point where we must acknowledgement that disturbance of any part is the manifestation of an inner disturbance is not a local confusion of certain muscles or of certain group of nerves, or arteries, or even of the mind itself; but that it is an expression of the whole disturbance manifesting itself perhaps locally or in seemingly unrelated parts; It is an expression of the disturbed vital energy, and is a manifestation of the ma as a unit, and not of the separate parts of his body.
...Any disturbance of this vital energy immediately shows itself in lack of harmony through the outward manifestations of our beings; in other words, symptom. When harmonious functioning is disturbed, we get sickness as a result, and it has as its base and inception this lack of harmony in the flow of vital energy through the body. This is manifest in disease as it naturally developed because of disturbed vital force, and it develops also in disturbed vital force from the proving of remedies, showing the action of remedies and the very nature of the remedies themselves.....
In sec. 12 Hahnemann says- "It is the morbidly affected vital force alone that produce disease."
The Principles and Art of cure by Homoeopathy - Herbert A. Roberts, MD