The Mandukya Upanishad (Gaudapa Karika and Shankara Bhashya)
Mandukya Karika, verse 2.34
This is verse 2.34 of the Mandukya Karika English translation, including commentaries by Gaudapada (Karika), Shankara (Bhashya) and a glossary by Anandagiri (Tika). Alternate transliteration: Māṇḍūkya-upaniṣad 2.34, Gauḍapāda Kārikā, Śaṅkara Bhāṣya, Ānandagiri Ṭīkā.
Sanskrit text, IAST transliteration and English translation
नाऽऽत्मभावेन नानेदं न स्वेनापि कथंचन ।
न पृथङ्नापृथक्किंचिद् इति तत्त्वविदो विदुः ॥ ३४ ॥
nā''tmabhāvena nānedaṃ na svenāpi kathaṃcana |
na pṛthaṅnāpṛthakkiṃcid iti tattvavido viduḥ || 34 ||
34. This manifold does not exist as identical with Ātman nor does it ever stand independent by itself. It is neither separate from Brahman nor is it non-separate. This is the statement of the wise.
Shankara Bhashya (commentary)
Why is non-duality called the highest bliss? One suffers from misery when one finds differences in the form of multiplicity, i.e., when one finds an object separate from another. For1 when this manifold of the universe with the entire relative phenomena consisting of Prāṇa, etc., imagined in the non-dual Ātman, the Ultimate Reality is realised to be identical with the Ātman, the Supreme Reality, then alone multiplicity ceases to exist, i.e., Prāṇa, etc., do not appear to be separate from Ātman. It2 is just like the snake that is imagined (to be separate from the rope) but that does no longer remain as such when its true nature is known with the help of a light to be nothing but the rope. This manifold (Idam) does never really exist as it appears to be, that is to say, in the forms of Prāṇa, etc., because3 it is imaginary just like the snake seen in the place of the rope. Therefore different objects, such as Prāṇa, etc., do not exist as separate from one other as a buffalo appears to be separate from a horse. The idea of separation being unreal, there is nothing which exists as separate from an object of the same nature or from other objects (of different nature). The Brāhmaṇas, i.e., the Knowers of Self, know this4 to be the essence of the Ultimate Reality. Therefore the implication of the verse is that non-duality alone, on account of the absence of any cause that may bring about misery, is verily the (highest) bliss.
Anandagiri Tika (glossary)
1 For, etc.—Does this insentient manifold exist as one with Ātman? This position is untenable as the sentient Ātman and insentient universe can never be identical. For, if it be admitted that the manifold is identical with Ātman which is one and without a second, then multiplicity cannot exist.
2 It is, etc.—The snake, which in the darkness appeared to be separate from the rope, is known with the help of a light, to be the same as the rope. The light does not show that the rope is identical with the snake, as such identity is an impossibility, but it reveals that the only thing that exists is the rope and even that which appeared as the snake in the dark was nothing but the rope. Similarly, Ātman alone exists and the phenomenon, which appears through ignorance to be separate from Ātman, is also Ātman from the standpoint of Truth.
3 Because—It is because the idea of separation is unreal. A pot is known only in relation to a cloth or another object. One cannot totally exclude another. Therefore the objects, that are perceived to exist, are not mutually independent from the standpoint of Truth. It is the non-dual Ātman alone which appears as multiple objects, having relations, through ignorance.
4 This—i.e., duality or multiplicity does never exist, as it cannt be demonstrated.