Why Do a Purification Retreat?
The reason why purification practices such as rainbow purification or Vajrasattva are done in sequestered retreat environment is because purification is not pretty. I do not recall which purification is the least pretty. So, we enter retreat with determination and some important purpose to do strong purification practice. Or perhaps your lama is giving instructions and initiation into a deity such as Vajrasattva, Buddha of purification that includes commentary and group or private meditation away from your own home.
There may be a special obstacle you are experiencing such as a personal health problem or a meditation obstacle that not amenable to daily meditation. Some meditators will do a retreat for the health of a family member, success for their monastery, or even worldly goals such as personal success.
The state of mind to hold while on purification must be more careful than you might think. It is not a good idea to charge at the obstacle like a bull toward a red cape. By directly confronting the obstacle that is hiding in the mind and uncovering it might stir up energies at a time when you are already disturbed by the obstacle. That is why reliance and refuge in the Buddha, dharma and sangha, the three jewels, is extremely important so the meditator does not arouse fear and anger when the obstacle start to break up. We focus on the three jewels as valid inner objects instead of looking at our self.
If we misuse the energy that is freed from purification practice, we could become rigid in the mind. An unskillful meditator might even become confused and lose refuge, entering into blaming others or feeling disrespected. We need to preserve a skillful portion of our mind that remains objective. Purification roils the unaligned confused energies like dirty, murky water that become useless to drink. That is why we have to be careful with the mind during this time and not have any extra pressure or stress. Purification is not easy!
Be very careful with yourself on retreat. Keep steady balanced mind, and do not think that someone is trying to disrespect you or start blaming somebody or blaming the food. Maybe we should leave food issues in place so that at least we would have something to blame rather than people. Most importantly, do not cause sorrow to yourself by listening to your own ideas and feelings that you are no good or you that someone is saying something about you, which is not true.
True skill when working with the mind by using the mind comes only with practice. Eventually, the meditator does not listen to their own mental ramblings and goes on steadily toward the state of clarity achieving a new sense of spaciousness and peace. Soon, new levels are ready to be clarified. Such is the life of a real practitioner.