How to be Pure of Mind

"If a man should stand by a limpid pure spring, and curse it, the spring never ceases sending up potable water; and if he should cast clay into it or filth, it will speedily disperse them and wash them out, and will not be at all polluted. How then shalt thou possess a perpetual fountain?" How will you be pure of mind, wholesome of spirit, unblemished by nonsense, and cleansed of the corruptions by which your equanimity is stained? You must look within, and dig your own fountain.