“The Self is subtler than the subtle, greater than the great; It dwells in the heart of each living being. He who is free from desire and free from grief, with mind and senses tranquil, beholds the glory of the Atman. Although this Atman dwells in the heart of every living being, yet It is not perceived by ordinary mortals because of Its subtlety. It cannot be perceived by the senses; a finer spiritual sight is required. The heart must be pure and freed from every unworthy selfish desire; the thought must be indrawn from all external objects; mind and body must be under control; when the whole being thus becomes calm and serene, then it is possible to perceive that effulgent Atman. It is subtler than the subtle, because It is the invisible essence of every thing; and It is greater than the great because It is the boundless, sustaining power of the whole universe; that upon which all existence rests.” /Katha Upanishad Part2/XX