Sri Aurobindo translates Mundaka Upanishad, Chapter 3, Section 1, Verse 4: “This is the life in things that shines manifested by all these beings; a man of knowledge coming wholly to know this, draws back from creeds and too much disputings. In the Self his delight, at play in the Self, doing works, — the best is he among the knowers of the Eternal.”
As a follow up to the prior verse, the Upanishad clarifies that the Brahman is manifest in all the beings and forms of the world we experience around us. The seer experiences the oneness and thereby recognizes that the fragmented understanding of the mind leads to disputes based in partial and incomplete knowledge and understanding. Philosophies, creeds, religions, ways of life are all simply existence seen from the differing perspectives that arise as the mind perceives things from the individual, not the universal or transcendent standpoint. Logical argument, reasoned disagreements, emotional differences all arise from this limited perspective. When the seeker achieves the divine standpoint, all these things are seen as elements of the complex tapestry of individual forms woven by the divine manifestation, and they are all one and unified.
It must also be noted that the Upanishad also makes a point of re-integrating the outer existence in the final sentence of this verse. “…at play in the Self, doing works, — the best is he among the knowers of the Eternal.”. While an exclusive concentration may be needed initially to achieve the shift of standpoint to the Divine standpoint, eventually the seeker must reintegrate the reality of the outer world and works as also being the Brahman. Those who are fixated on the outer world operate in a form of ignorance. Those who are fixated solely on the Eternal and lose sight of the omnipresent reality of the creation that IS the Brahman also operate under a limitation. This echoes the sentiment we find in the Isha Upanishad as well. Some commentators hold that nothing here indicates any reality for the outer world or the idea of integrating the outer world with the experience of the Eternal. We believe the plain language about “doing works” combined with the fact that it is a householder receiving the teaching, implies a non-dual approach that recognizes the world also as Brahman, and not simply an illusion to be discarded.
The Mundaka Upanishad has a lot of emphasis on the achievement of the shift to the Divine standpoint and obviously making this happen is a major focus and emphasis for the seeker of realisation. In this verse, the seeker is reminded to not create a duality, but recognize the inherent oneness of the Eternal and the manifested universe, and to participate in that process with full knowledge.
Sri Aurobindo, The Upanishads, Mundaka Upanishad, pp. 193-210