The subconscient is the home, in the earth consciousness, of the quality of Tamas, just as the vital manifestation is the natural home of the quality of Rajas, and the mental level and above would be the natural home of the quality of Sattwa. These are all mixed up in the human being, interact with each other and constantly exert their influence to provide a very mixed result. None of the human instruments is entirely pure either as to a specific quality or as to its power of expression or action. Until a complete transformation has taken place, there will always be some amount of dilution to the pure action of any of these forces.
An objective of the integral yoga, then, is to direct the aspiration to the higher levels above the mind that bring with them the purer action of Sattwa, in the form of peace, knowledge, joy, harmony and lightness of being, and use that higher formation and power to purify and uplift the mind-life-body complex and eventually infuse the higher light into the realm of the subconscient, as the evolutionary cycle develops and progresses. This will shift the status of the earth-consciousness to a next higher vibratory level.
Sri Aurobindo writes: “The subconscient is a dark and ignorant region, so that it is natural that the obscurer movements of the Nature should have more power there. It is so indeed with all the lower parts of the nature from the lower vital downwards. But it does send up good things also though more rarely. It has in the course of the sadhana to be illumined and made a support of the higher consciousness in the physical nature instead of a basis of the instinctive lower movements.”
“The subconscient is to be penetrated by the light and made a sort of bed-rock of truth, a store of right impressions, right physical responses to the Truth. Strictly speaking, it will not be subconscient at all, but a sort of bank of true values held ready for use.”
“So long as there is not the supramental change down to the subconscient, complete and full, the lower nature has always a hold on some part of the being.”
Sri Aurobindo, Integral Yoga: Sri Aurobindo’s Teaching and Method of Practice, Chapter 9, Transformation of the Nature, Transformation of the Subconscient, pp. 262-267