The fourth mental purification is to free oneself from a form and have the sense of the abstract. Everything suggests to the eye a form, everything; even so much that if the name of a person whom one has never seen is mentioned, one makes a form of him. Even such things as fairies and spirits and angels, as soon as they are mentioned, are always pictured in a certain form. This is a hindrance to attaining the presence of the formless; and therefore this mental purification is of very great importance. Its purpose is to be able to think of an idea without form. No doubt this is only attained by great concentration and meditation, but once it is attained it is most satisfactory.