Sin and virtue would have no effect upon a person if the mind did not take impressions; nor would good and evil thoughts work on the external body if impressions were erased from the mind immediately. The sages in the East have, therefore, mastered concentration, that by its help they might be able to wipe off all that is undesirable, since it is human to err. But one arrives at this power by collecting all the good one can in the mind, so that evil may be naturally repulsed. By constantly doing so one acquires mastery.