Sri Aurobindo translates Mundaka Upanishad, Chapter 2, Section 2, Verse 12: “All this is Brahman immortal, naught else; Brahman is in front of us, Brahman behind us, and to the south of us and to the north of us and below us and above us; it stretches everywhere. All this is Brahman alone, all this magnificent universe.”
There can be no clearer statement about Brahman as the sole Existent who manifests the entire universe and everything we experience. There is this one Brahman; there is no other. Dualistic views of the universe, which indicate there is a Creator who fashions the universe and observes it from outside are specifically rebuffed. At the same time, those who speak of the universe being something of an illusion and who must renounce the world in order to find the Divine are also cautioned here. Earlier in the Mundaka Upanishad it may have appeared that renunciation was the goal. With this verse, it is now clear that renunciation is a tactic, not a goal, and that its purpose is to orient the understanding and focus of the seeker. Once the standpoint of the seeker has been altered, the reality of the universe as Brahman can now be affirmed.
In The Life Divine, Sri Aurobindo resolves the tension between the materialist view that the world is real and the Divine is unreal versus the renunciate’s view that the Divine is real and the world unreal, with the concept of “reality omnipresent”. In this view, the world is Brahman, and thus, not to be denied its significance, while at the same time, Brahman is not defined or limited by the framework of the manifested universe; rather the specific forms and forces are expressions of Brahman, without being limiting factors.
Sri Aurobindo, The Upanishads, Mundaka Upanishad, pp. 193-210