At the basis of homeopathy is the belief that the body is ruled by a spiritual, animating force.  Hahnemann states:  

In the healthy condition of man, the spiritual vital force (autocracy), the dynamis that animates the material body (organism), rules with unbounded sway, and retains all the parts of the organism in admirable, harmonious, vital operation, as regards both sensations and functions, so that our indwelling, reason-gifted mind can freely employ this living, healthy instrument for the higher purpose of our existence.... 
 ...The material organism, without the vital force, is capable of no sensation, no function, no self-preservation, it derives all sensation and performs all the functions of life solely by means of the immaterial being (the vital principle) which animates the material organism in health and in disease (Organon, sixth edition)

Hahnemann believed that the cause of disease is  the disturbance of this vital or life force.   Disturbances in the vital force manifest themselves as specific symptoms.  The Law of Susceptibility deals with the invasion of the body by diseases. The Law implies that that a negative state of mind attracts disease entities called miasms to enter and/or invade the body.  Miasms can be acquired acutely or they can be congenital or latent, until some negative experience or normal aging trigger their appearance as a symptom and then as disease.

Hahnemann argues that specific treatment of such symptoms by opposing their action, as in conventional medicine, is not useful in treating disease because the disturbance in the vital force remains.  Only correction of the underlying disturbance in the vital force can cure disease.