In a well-stocked pharmacy, one sees an impressive variety of medicines used to treat all types of illness.
The pharmacist will inform the visitor that only a qualified expert is allowed to dispense medications. Also, if a patient is to recover from his illness, he must take the medicine precisely as instructed by an expert.
This situation has an analogue in the spiritual realm. Each of us has been sent to this world by the Al-mighty to "heal" or refine ourselves with the remedies that He has provided - the Torah and mitzvos.
However, we still require the services of a "pharmacist," a teacher to advise us and guide us to the correct medications. Without the skillful judgment of such a person, we may select the wrong "cure" and seriously endanger our health.
It is important to keep in mind that once the medicine is in our possession and we know the proper dosage, we must not procrastinate or make excuses for not taking it. Obviously, one can recover only if one takes the remedy as prescribed. Similarly, we can fulfill our earthly mission only if we "take our prescribed medicine" (complete the spiritual tasks assigned to us).
The operations of a pharmacy provide another interesting insight. One can even find vials of poison on a drugstore's shelves! The pharmacist informs us of a paradoxical fact: minute amounts of certain poisons that would harm a healthy person can actually help cure some illnesses!
There are instances when one must dispense small amounts of "poison." For example, although we are taught never to insult or embarrass another person, we must nevertheless refuse a dinner invitation if the meal will not be kosher.
In addition, there are times when a person must gently rebuke a friend who is violating the dictates of the Torah (particularly if he believes that the friend will heed his words).
Perhaps this small dose of "poison" will be the remedy that heals the person.
Igros Kodesh of the Rebbe, Vol. 3, p. 145