All that exists lives on its own element, springs from its own element, and returns to its own element. So earth to earth, water to water, fire to fire and air to air.
Purification means to make a certain object itself, nothing added, nothing foreign attached to it which does not belong to it.

These two rules make one understand the process by which the mind could be nourished and purified. The mind is nourished by thoughts and impressions that are harmonious and productive of beauty and which result in satisfaction, for harmony is the nature of the soul, beauty is its source and goal, and by harmony and beauty the mind is nourished as it is made of harmony and beauty. And the same elements are needed to purify the mind of all undesirable thoughts and impressions, harmony as water and beauty as soap, purifying the mind of all thoughts which are void of harmony and beauty.

The first thing in purifying the mind is to be able to discern the foreign element there. As all that is foreign to the body does not agree with the body, making it ill, so all that is foreign to the mind disturbs the peace of the mind, and it is that which proves that it does not belong to the mind. Such things are worry, anxiety, fear, sorrow, or any sort of disturbance that takes away the tranquility of the mind, preventing it from experiencing that joy and peace for which it longs and in which alone is its satisfaction.

There are many who do not know the importance of keeping the mind in a pure and harmonious condition, and the few who know it find it difficult to bring about better conditions in practical life. In the first place it is difficult to accomplish outward duties, to answer the demands of life, and yet to keep the mind in perfect tranquility. It needs the knowledge of purifying the mind of all external influences.

And the way one can manage it can be said in a few words: to throw away disharmony by the power of harmony and to wash away all that lacks beauty by preserving the great power of beauty within oneself.