Every principle that applies to the body's healing has its counterpart in the healing of the soul. The body and soul are each a component of the whole human being, who is in turn a universe in microcosm.
To illustrate this concept the Previous Rebbe took an example from the field of medicine, when he received an injection from a physician.
At that time, before giving an injection, medical practitioners would go to great lengths to ensure the cleanliness of their instruments. The doctor and his assistants would don white garments. They would wash their hands thoroughly and check their nails, lest there be some accumulation of dirt. Finally, they would pour alcohol over the tips of their fingers to remove any speck of impurity.
Following these preparations, the medical team would cleanse the treatment area, removing any bacteria present. Although the patient would be clean, they would follow the procedure that, prior to piercing the flesh, the surrounding skin had to be scrubbed with a cleansing formula to ensure that no bacteria could enter along with the medication.
Among chassidim there is a practice known as a "farbrengen," where people gather to hear and share words of inspiration and to sing melodies which express the inner feelings of the heart. Its goal is for the speakers to inspire the participants to refine their behavior and improve their spiritual health. The focus is often given to the importance of designating fixed times for the study of Torah, and applying the principles derived from such study for self-improvement.
The purpose of the gatherings, like the injection, is the well-being of another person. In fact the warmth of the ideas and the beauty of the melodies have tremendous positive effects on the participants. Nevertheless, it is sometimes necessary to use harsh, cutting words to pierce the skin of the one in need of guidance, in order for the message to penetrate his defenses and have its desired effect.
As with the medical injection, considerable precautions must be taken by the speakers to ensure the cleanliness of their motives and the purity of their methods. The person receiving the spiritual "injection" must be thoroughly prepared. All this is essential to ensure that no dirt can enter when a person's skin is open and he is vulnerable.
Igros Kodesh of the Previous Rebbe, Vol. 3, p. 291ff.