nārāyaṇaḥ sa bhagavān
āpas tasmāt sanātanāt
yoga-nidrāṁ gatas tasmin
sahasrāṁśaḥ svayaṁ mahān
saḥ bhagavān – that very Mahā-Viṣṇu Bhagavān, the first of the puruṣa-avatāras; nārāyaṇaḥ – is renowned in the illusory universe by the name Nārāyaṇa; saṅkarṣaṇa-ātmakaḥ – and is originally manifested from Mūla-Saṅkarṣaṇa in Goloka, via His expansion named Mahā-Saṇkarṣaṇa in the Vaikuṇṭha planets, which are situated within the spiritual sky; tasmāt sanātanāt – from that eternal Lord; kāraṇārṇaḥ nidhiḥ āpaḥ – the vast waters of the Causal Ocean; āviḥ āsīt – become manifest; gataḥ – (then) entering; yoga-nidrām – into samādhi upon the bliss of His own intrinsic form and nature; tasmin – upon those waters; svayam mahān – and that Supreme Personality of Godhead; sahasra-aṁśaḥ – accepts many thousands of expansions as His avatāras.
This Mahā-Viṣṇu is celebrated within the world of māyā by the name “Nārāyaṇa.” The water of the Causal Ocean has emanated from this eternal puruṣa. He is Bhagavān, the supreme predominator, possessed of thousands of plenary portions, although He is Himself a plenary portion of the Saṅkarṣaṇa of Paravyoma. The eternal puruṣa takes shelter of mystic slumber and lies down in the vast waters of Virajā.
This Mahā-Viṣṇu reclines in the causal waters. He is called the first puruṣa-avatāra, and this particular verse is about Him, from whom the water of the Causal Ocean has emanated. He is called Nārāyaṇa because He lies down in this water (nāra means “water,” and ayana means “shelter” or “resting place”). He is a partial avatāra of Mahā-Saṅkarṣaṇa in Vaikuṇṭha. The Saṅkarṣaṇa in the chamber of Goloka, who was described earlier, is Mūla-Saṅkarṣaṇa, His plenary portion in the second quadruple expansion in Vaikuṇṭha is called Mahā-Saṅkarṣaṇa, and Kāraṇodakaśāyī Mahā-Viṣṇu is an expansion of this Mahā-Saṅkarṣaṇa. It is His pastime to create the Causal Ocean and lie down in it in mystic slumber, which is a state of trance induced by His own intrinsic, ecstatic nature (svarūpānanda-samādhi). It is stated in the Viṣṇu Purāṇa (1.4.6):
āpo nārā iti proktā
āpo vai nara-sūnavaḥ
tasya tā ayanaṁ pūrvaṁ
tena nārāyaṇaḥ smṛtaḥ
Āpa means nāra, which in turn is understood to mean both water and the living entity (jīva). Because Bhagavān is the supreme shelter of both, He is called Nārāyaṇa.