On Mundaka Upanishad: Immortality is when there is just sky and skyness

Following is an excerpt from a samvaad (dialogue) session with Acharya Prashant.

यस्मिन्द्यौः पृथिवी चान्तरिक्षमोतं मनः सह प्राणैश्च सर्वैः ।
तमेवैकं जानथ आत्मानमन्या वाचो विमुञ्चथामृतस्यैष सेतुः ॥

yasmindyauḥ pṛthivī cāntarikṣamotaṃ manaḥ saha prāṇaiśca sarvaiḥ
tamevaikaṃ jānatha ātmānamanyā vāco vimuñcathāmṛtasyaiṣa setuḥ

He in whom are inwoven heaven and earth and the mid region, and mind with all the life currents, Him know to be the one Self; other words put away from you: this is the bridge to immortality.

~ Verse 2.2.5

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Acharya Prashant (AP): “He in whom are inwoven heaven and earth and the mid-region,” everything between heaven and earth means everything in total, “and mind with all the life currents,” mind with all its stuff, “Him know to be the one Self; other words put away from you: this is the bridge to immortality.”

To simplify: He in whom are inwoven, contained heaven and earth and everything in between — meaning the entire universe — He who contains the entire universe and the mind with all its currents of thoughts and passions and experiences, Him know to be one Self. ‘Self’ here refers to Ātman. “Put other words away from you: this is the bridge to immortality; this is how you keep death away from yourself.”

What is the relationship between immortality, deathlessness, and knowing the Ātman as the container of the material and the mental world? Not that they are really distinct, but still. So, what is the relation between knowing Ātman as the container of the world, keeping all other thoughts aside, and immortality? The verse is stretching upon these three things and connecting them.

First: the Ātman is the envelope, the container of the entire universe, of everything that appears, everything that is perceptible. The Ātman contains it; the Ātman is the sky in which the activities of…