Concentration is taught by the mystics in order to exercise the will, making it capable of making use of all faculties. A person with will-power can remember what he wishes to remember and can forget what he wishes to forget. All things that deprive one of one's freedom in life are undesirable. The mind must be free from all bad impressions of life, which take away the rest and peace of life. By concentration one is able to hold a certain thought one desires and to keep away all other thoughts, and when one is able to keep away all the thoughts one does not wish to think about, it becomes easy to throw away the impressions of years, if one wishes to forget them. Bad impressions, however old and intimate, are like rubbish accumulated, which should be removed in order to make the house clean.