The faculty of the mind that engages in thought, while part of the lower nature of body-life-mind, is utilized to help achieve the separation of the witness Purusha from the physical and vital portions of the being, as has been previously described. In the end, however, the seeker must be prepared to go beyond this faculty to achieve the higher spiritual standpoint. The thought-mind is also contaminated in its functioning by the vital Prana and thus, the human being, relying on this thought-mind, forms ideas, opinions and plans that are framed, biased or colored by the action of desire.
Sri Aurobindo points out: “The Purusha, having used the thought-mind for release from identification with the life and body and with the mind of desire and sensations and emotions, will turn round upon the thought-mind itself and will say ‘This too I am not; I am not the thought or the thinker; all these ideas, opinions, speculations, strivings of the intellect, its predilections, preferences, dogmas, doubts, self-corrections are not myself; all this is only a working of Prakriti which takes place in the thought-mind.’ Thus a division is created between the mind that thinks and wills and the mind that observes and the Purusha becomes the witness only; he sees, he understands the process and laws of his thought, but detaches himself from it. Then as the master of the sanction he withdraws his past sanction from the tangle of the mental undercurrent and the reasoning intellect and causes both to cease from their importunities. He becomes liberated from subjection to the thinking mind and capable of the utter silence.”
The development of this stage can be disconcerting, particularly to those who have a highly developed intellectual capacity and who have come to identify and take ownership of that capacity in their lives. Yet it remains essential to be able to rise above the entire mechanism of the lower nature, and the mind is part of that mechanism.
“For perfection there is necessary also the resumption by the Purusha of his position as the lord of his Nature and the will to replace the mere mental undercurrent and intellect by the truth-conscious thought that lightens from above. But the silence is necessary; in the silence and not in the thought we shall find the Self, we shall become aware of it, not merely conceive it, and we shall withdraw out of the mental Purusha into that which is the source of the mind. But for this withdrawal a final liberation is needed, the release from the ego-sense in the mind.”
Sri Aurobindo, The Synthesis of Yoga, Part Two: The Yoga of Integral Knowledge, Chapter 8, The Release from the Heart and the Mind, pp. 339-340