The Buddhist texts describe the healing mechanism underlying vipassanā in great detail. Lacking sufficient knowledge and the right vocabulary, I present my broad understanding in plain English.
Misery: In one of the discourses, S N Goenka mentions that two kinds of events in our lives make us miserable. One, when something unwanted happens, we react with aversion towards such events. Two, when something that we want is not happening, we react with craving for such events. Thus craving and aversion are at the root of our misery.
What are the signs of being miserable? Outwardly, our demeanor smacks of some combination of anger, hatred, ill-will, passion, fear end ego. Internally, our mind quickly meanders towards thoughts pertaining to the event. At the same time, our breath becomes shorter and harder. Also, we get sensations at different parts of our body. In the normal course of life, many of these sensations are imperceptible but we can develop our ability to observe them by practicing vipassanā.
Depending upon the intensity of our misery, we dwell in it for a few seconds or minutes or hours or days or weeks or months or years or lifetimes.
A miserable person makes others miserable.
Non-reaction: It is important to realize that events are merely events, many of these are out of our control. However, our reaction is under our control. We can learn not to react with aversion towards unwanted events and not to react with craving for events that we want to happen but are not happening. Vipassanā meditation helps us cultivate such abilities of non-reaction. Let us see how.
During the 10-day course, especially from the fourth day onwards, we start remembering events that make us miserable. Concomitant with these memories are sensations that arise in our body. In Buddhist literature, the word saṅkhāra (which I loosely understand as 'ability to react') explains this phenomenon. S N Goenka says that a steady stream of our "old stock of saṅkhāras" comes up from the unconscious to the conscious. By merely observing the sensations that result, without craving or aversion, we change the habit pattern of our mind and neutralize these saṅkhāras, thereby healing us.
Many people report that after the 10-day course, events that bothered them earlier do not bother them any more. They become more peaceful and pleasant, such changes being noticeable in their demeanor by others.
Vipassanā meditation would actually take you a step beyond non-reaction to events. You shall start generating compassion for even those who harm you.
Compassion: In one of his discourses, S N Goenka mentions that as we make progress in vipassanā, we shall start generating compassion for an aggressor because we would understand that the aggressor is usually far more miserable than the victim. This will helps us understand how Jesus Christ, for example, had great love and compassion for people who were physically harming him. This is a powerful teaching to internalize.
How do we start generating such compassion? I feel that the mechanism is somewhat as follows. The practice of mettā-bhāvanā (cultivation of loving-kindness) for everybody helps us. Also, during vipassanā, we remember our past where we generated misery for ourselves and for others, for example, due to our own anger and agitation. By seeing ourselves in the role of an aggressor, we forgive ourselves, then start forgiving others and generate compassion for them.
Contrast with Therapy: In psychotherapy and hypnotherapy, the healing mechanism is to come to terms with painful or distressing events in earlier life by revisiting those events, reliving that experience and seeing these events from a third person's perspective. Sometimes, we actually forget the events themselves but we retain abstract anger or abstract fear in us and our mind gets trained to react in unhealthy ways in certain situations. A therapist helps us change the habit pattern of our mind so that we no longer react with emotions like anger, hatred and fear in such situations.
In vipassanā, one goes through a therapeutic process similar to psychotherapy or hypnotherapy, but without a specialist guiding our thoughts. First, the mind is made tranquil and sharp with breath meditation. Then, when vipassanā is practiced, memories and sensations associated with painful or distressing events in our lives automatically start becoming prominent; they arise from the unconscious to the conscious. Maintaining the practice from the fifth day onwards is particularly challenging because we have stirred a storm that makes our mind turbulent. At the same time, through breath meditation, we have also acquired the ability to weather the storm by remaining unperturbed. So with perseverance, during vipassanā meditation, we observe the storm as it arises and passes away, with equanimity, without aversion or craving, thereby training our mind not to react. Such purification of the mind not only heals us of misery caused by past events but also prepares for the future. We learn how to face the vicissitudes of life with equanimity.
May all be peaceful.