Sri Aurobindo
Letters of Sri Aurobindo
Volume III - Part 4
The soul, the psychic being, is in direct touch with the divine Truth, but it is hidden in man by the mind, the vital being and the physical nature (manas, prāṇa, anna of the Taittiriya Upanishad). One may practise Yoga and get illuminations in the mind and the reason; one may conquer power and luxuriate in all kinds of experiences in the vital; one may establish even surprising physical siddhis; but if the true soul-power behind does not manifest, if the psychic nature does not come into the front, nothing genuine has been done. In this Yoga, the psychic being is that which opens the rest of the nature to the true supramental light and finally to the supreme Ananda. Mind can open by itself to its own higher reaches; it can still itself and widen into the Impersonal; it may too spiritualise itself in 
some kind of static liberation or Nirvana; but the supramental cannot find a sufficient base in spiritualised mind alone. If the inmost soul is awakened, if there is a new birth out of the mere mental, vital and physical into the psychic consciousness, then this Yoga can be done; otherwise (by the sole power of the mind or any other part) it is impossible. If there is a refusal of the psychic new birth, a refusal to become the child new born from the Mother, owing to attachment to intellectual knowledge or mental ideas or to some vital desire, then there will be a failure in the sadhana.