The highest contribution which mysticism can make is to afford its votaries glimpses of that grand substratum of the universe which we may call the Overself. These glimpses reveal It in the pure unmanifest non-physical essence that It ultimately is. They detach It from the things, creatures, and thoughts which make up this world of ours, and show It as It is in the beginning, before the world-dream made its appearance. Thus mysticism at its farthest stretch, which is Nirvikalpa samadhi, enables man to bring about the temporary disappearance of the world-dream and come into comprehension of the Mind within which, and from which, the dream emerges. The mystic in very truth conducts the funeral service of the physical world as he has hitherto known it, which includes his own ego. But this is as far as mysticism can take him. It is an illuminative and rare experience, but it is not the end. For the next task which he must undertake if he is to advance is to relate his experience of this world as real with his experience of the Overself as real. And this he can do only by studying the world's own nature, laying bare its mentalistic character and thus bringing it within the same circle as its source, the Mind. If he succeeds in doing this and in establishing this relation correctly, he will have finished his apprenticeship, ascended to the ultimate truth, and become a philosopher. Thenceforward he will not deny the world but accept it.
The metaphysician may also perform this task and obtain an intellectual understanding of himself, the world, and the Overself. And he has this advantage over the mystic, that his understanding becomes permanent whereas the mystic's rapt absorption must pass. But if he has not passed through the mystical exercises, it will remain as incomplete as a nut without a kernel. For these exercises, when led to their logical and successful issue in Nirvikalpa samadhi, provide the vivifying principle of experience which alone can make metaphysical tenets real.
From all this we may perceive why it is quite correct for the mystic to look undistractedly within for his goal, why he must shut out the distractions and attractions of earthly life in order to penetrate the sacred precinct, and why solitude, asceticism, meditation, trance, and emotion play the most important roles in his particular experience. What he is doing is right and proper at his stage but is not right and proper as the last stage. For in the end he must turn metaphysician, just as the metaphysician must turn mystic and just as both must turn philosopher--who is alone capable of infusing the thoughts of metaphysics and the feelings of mysticism into the actions of everyday practical life.
-- Notebooks Category 20: What Is Philosophy? > Chapter 4: Its Realization Beyond Ecstasy > # 115
-- Perspectives > Chapter 20: What Is Philosophy? > # 50