Recognizing the need to focus entirely on the Brahman, some paths of spiritual development preach abandonment of the life in the world. They regard the world as a distraction, an illusion, a secondary phenomenon; for them, the real essence is the “one without a second”. Yet there is another, equally important truth enunciated in the texts, “all this is the Brahman”. The mental consciousness, which has as a core strength the ability to analyze and separate into constituent parts, seizes on these two as opposites and some take the route of accepting the first, while others take the route of accepting the second, as their primary guideline. In reality, the two are aspects of the very same truth, and should be understood together. One without a second does not mean the world is unreal, it means the world itself “all this” is the Brahman. The realisation of the Oneness of Brahman and the outer world implies that we need to learn how to experience Brahman right here, in the midst of the activities of mind, life and body.
Sri Aurobindo observes: “The Mind is cosmic, one in all the universe; so too are the Life, and the Sense, so too is Matter of the body; and when they exist in and for the Brahman only, they will not only know this but will sense, feel and live in that universal unity. Therefore to whatever thing they turn which to the individual sense and mind and life seems now external to them, there also it is not the mere form of things which they will know, think of, sense, embrace and enjoy, but always and only the Brahman. Moreover, the external will cease to exist for them, because nothing will be external but all things internal to us, even the whole world and all that is in it. For the limit of ego, the wall of individuality will break; the individual Mind will cease to know itself as individual, it will be conscious only of universal Mind one everywhere in which individuals are only knots of the one mentality; so the individual life will lose its sense of separateness and live only in and as the one life in which all individuals are simply whirls of the indivisible flood of Pranic activity; the very body and senses will be no longer conscious of a separated existence, but the real body which the man will feel himself to be physically will be the whole Earth and the whole universe and the whole indivisible form of things wheresoever existent, and the senses also will be converted to this principle of sensation so that even in what we call the external, the eye will see Brahman only in every sight, the ear will hear Brahman only in every sound, the inner and outer body will feel Brahman only in every touch and the touch itself as if internal in the greater body. The soul whose gods are thus converted to this supreme law and religion, will realise in the cosmos itself and in all its multiplicity the truth of the One besides whom there is no other or second. Moreover, becoming one with the formless and infinite, it will exceed the universe itself and see all the worlds not as external, not even as commensurate with itself, but as if within it.”
Sri Aurobindo, The Upanishads, Kena Upanishad and analysis, pg. 107, 177-183