यदर्चिमद्यदणुभ्योऽणु च यस्मिंल्लोका निहिता लोकिनश्च ।तदेतदक्षरं ब्रह्म स प्राणस्तदु वाङ्मनः ।तदेतत्सत्यं तदमृतं तद्वेद्धव्यं सोम्य विद्धि ॥ २ ॥
In plain words
That which is aflame and subtler than the subtle, in which the worlds and their inhabitants are set—that is Akṣara Brahman. It is Prāṇa; it is speech and Manas. That is Satya; that is Amṛta. That is to be pierced, gentle one—pierce it.
The commentators
Muṇḍakopaniṣadbhāṣyam· bhāṣya
ये च लोकिन लोकनिवासिन मनुष्यादय , चैतन्याश्रया हि सर्वे प्रसिद्धा , तदेतत् सर्वाश्रयम् अक्षर ब्रह्म स प्राण तदु वाङ्मन वाक्च मनश्च सर्वाणि च करणानि तदु अन्तश्चैतन्यम् , चैतन्याश्रयो हि प्राणेन्द्रियादिसर्वसघात , 'प्राणस्य प्राणम्' इति श्रुत्यन्तरात् । यत्प्राणादीनामन्तश्चैतन्य- मक्षर तदेतत् सत्यम् अवितथम् , अत अमृतम् अविनाशि तत् वेद्धव्य मनसा ताडयितव्यम् । तस्मिन्मनस समाधान कर्तव्यमित्यर्थ । यस्मादेव हे सोम्य, विद्धि अक्षरे चेत समाधत्स्व ॥
In plain words
Human beings and every other dweller in the worlds are known only because Caitanya, consciousness, supports them. The Akṣara-Brahman supports them all. It is Prāṇa; it is Vāk and Manas—speech, mind, and all the faculties—while within them it remains Caitanya itself. The whole gathering of Prāṇa, senses, and organs depends on that consciousness; another Śruti calls it “the Prāṇa of Prāṇa.” The Akṣara is the inner awareness within Prāṇa and all the rest. It is true and unfailing, immortal and undecaying, and it is the target to be struck with Manas. In other words, gather the mind wholly into it. Dear one, pierce the Akṣara; settle your Citta there.
Close to the Sanskrit
And the lokins—dwellers in the worlds, humans and others—are all known to rest upon Caitanya. This Akṣara-Brahman is the support of all. It is Prāṇa; it indeed is Vāk and Manas, speech and mind and all the karaṇas; it indeed is the Caitanya within. For the entire aggregate of Prāṇa, indriyas, and the rest rests upon Caitanya, as another Śruti says, “the Prāṇa of Prāṇa.” That Akṣara which is the inner Caitanya of Prāṇa and the rest is this satya, the unfailing, and therefore the immortal, the imperishable. It is to be pierced, struck by Manas. The meaning is that Manas must be concentrated in it. Therefore, dear one, pierce it; settle Citta in the Akṣara.