In the Taittiriya Upanishad, the Upanishadic seer takes the seeker through a series of meditations on the nature of Existence. The first stage that the seeker examines and realizes is that Matter is the Brahman, the foundation, the basis, the Truth of Existence, and without which nothing else could exist. Of course, as the seeker is asked to go back and reflect further, the truths of life energy, mind, the knowledge-will, and the bliss of existence successively are revealed and we get a more complete picture of the manifestation than the initial formulation of “matter is Brahman”. But still, we do not lose the substance of this realisation. It is not that it is wrong, but that it was simply not broadly enough understood. For indeed, Matter IS the Brahman.
Sri Aurobindo explains this concept as follows: “Brahman is not only the cause and supporting power and indwelling principle of the universe, he is also its material and its sole material. Matter also is Brahman and it is nothing other than or different from Brahman. If indeed Matter were cut off from Spirit, this would not be so; but it is, as we ahve seen, only a final form and objective aspect of the divine Existence with all of God ever present in it and behind it.”
The tendency of the human mind to fragment, divide, separate and analyse does us a disservice here as it creates this artificial distinction that treats matter as other than and separate from spirit. The spiritual development of consciousness has as one of its consequences the development of an awareness of integral Oneness that can both see the distinctions that Matter, Life and Mind create, as well as the underlying and informing Unity that is based on the principle of Oneness for all Existence.
reference: Sri Aurobindo, The Life Divine, Chapter 25, The Knot of Matter