SB 2.10.10

puruṣo ’ṇḍaṁ vinirbhidya
 yadāsau sa vinirgataḥ
ātmano ’yanam anvicchann
 apo ’srākṣīc chuciḥ śucīḥ
Synonyms: 
puruṣaḥ — the Supreme Person, Paramātmā; aṇḍam — the universes; vinirbhidya — making them each separately situated; yadā — when; asau — the same; saḥ — He (the Lord); vinirgataḥ — came out; ātmanaḥ — of Himself; ayanam — lying in place; anvicchan — desiring; apaḥ — water; asrākṣīt — created; śuciḥ — the most pure; śucīḥ — transcendental.
Translation: 
After separating the different universes, the gigantic universal form of the Lord [Mahā-Viṣṇu], which came out of the Causal Ocean, the place of appearance for the first puruṣa-avatāra, entered into each of the separate universes, desiring to lie on the created transcendental water [Garbhodaka].
Purport: 

After analysis of the living entities and the Supreme Lord, Paramātmā, the independent source of all other living beings, Śrīla Śukadeva Gosvāmī is now presenting the prime necessity for devotional service to the Lord, which is the only occupational business of all living entities. The Supreme Lord Śrī Kṛṣṇa and all His plenary portions and extensions of plenary portions are nondifferent from one another, and thus the supreme independence is in each and every one of them. In order to prove this, Śukadeva Gosvāmī (as promised to King Parīkṣit) describes herein the independence of the puruṣa-avatāra Personality of Godhead, even in the sphere of the material creation. Such activities of the Lord are also transcendental, and therefore they are also līlā, or pastimes, of the Absolute Lord. Such pastimes of the Lord are very conducive to the hearers for self-realization in the field of devotional service. Some may argue, “Then why not relish the transcendental līlā of the Lord as exhibited in the land of Mathurā and Vṛndāvana, which are sweeter than anything in the world?” Śrīla Viśvanātha Cakravartī Ṭhākura replies that the pastimes of the Lord in Vṛndāvana are meant to be relished by advanced devotees of the Lord. Neophyte devotees will misunderstand such supreme transcendental activities of the Lord, and therefore the Lord’s pastimes in the material sphere related to creation, maintenance and destruction are verily relishable by the prākṛta, or mundane devotees of the Lord. As the yoga system mainly based on bodily exercises is meant for the person who is too much attached to the bodily conception of existence, similarly the Lord’s pastimes related to the creation and destruction of the material world are for those who are too materially attached. For such mundane creatures the functions of the body and the functions of the cosmic world through physical laws in relationship with the Lord are also therefore included in understanding of the lawmaker, the Supreme Personality of Godhead. The scientists explain the material functions by so many technological terms of material law, but such blind scientists forget the lawmaker. The Śrīmad-Bhāgavatam points out the lawmaker. One should not be amazed by the mechanical arrangement of the complicated engine or dynamo, but one should praise the engineer who creates such a wonderful working machine. That is the difference between the devotee and the nondevotee. Devotees are always full with praising the Lord, who directs the physical laws. In the Bhagavad-gītā (9.10) the direction of the Lord upon the material nature is described as follows:

mayādhyakṣeṇa prakṛtiḥ
 sūyate sacarācaram
hetunānena kaunteya
 jagad viparivartate

“The material nature full of physical laws is one of My different energies; therefore it is neither independent nor blind. Because I am transcendentally all-powerful, simply by My glancing over material nature, the physical laws of nature work so wonderfully. The actions and reactions of the physical laws work on that account, and thus the material world is created, maintained and annihilated again and again.”

Men with a poor fund of knowledge, however, become astonished by studying the physical laws both within the construction of the individual body and within the cosmic manifestation, and foolishly they decry the existence of God, taking it for granted that the physical laws are independent, without any metaphysical control. The Bhagavad-gītā (9.11) replies to this foolishness in the following words:

avajānanti māṁ mūḍhā
 mānuṣīṁ tanum āśritam
paraṁ bhāvam ajānanto
 mama bhūta-maheśvaram

“The foolish men [mūḍhāḥ] do not know the Personality of Godhead in His eternal form of bliss and knowledge.” The foolish man thinks of the transcendental body of the Lord as something like his own, and therefore he cannot think of the unlimited controlling power of the Lord, who is not visible in the acting of the physical laws. The Lord is, however, visible to the naked eyes of people in general when He descends Himself by His own personal potency. Lord Kṛṣṇa incarnated Himself as He is and played very wonderful parts as the Lord Himself, and the Bhagavad-gītā concerns such wonderful actions and knowledge. Yet foolish men will not accept Lord Kṛṣṇa as the Supreme Lord. Generally they consider the infinitesimal and infinite features of the Lord because they themselves are unable to become either the infinitesimal or the infinite, but one should know that the infinite and infinitesimal sizes of the Lord are not His highest glories. The most wonderful manifestation of the Lord’s power is exhibited when the infinite Lord becomes visible to our eyes as one of us. Yet His activities are different from those of the finite beings. Lifting a mountain at the age of seven years and marrying sixteen thousand wives in the prime of His youth are some of the examples of His infinite energy, but the mūḍhas, after seeing them or hearing about them, decry them as legendary and take the Lord as one of them. They cannot understand that the Lord Śrī Kṛṣṇa, although in the form of a human being by His own potency, is still the Supreme Lord with full potency as the supreme controller.

When, however, the mūḍhas give submissive and aural reception to the messages of the Lord as in the Śrīmad Bhagavad-gītā or in the Śrīmad-Bhāgavatam through the channel of disciplic succession, such mūḍhas also become devotees of the Lord by the grace of His pure devotees. And for this reason only, either in the Bhagavad-gītā or in the Śrīmad-Bhāgavatam, the pastimes of the Lord in the material world are delineated for the benefit of those men with a poor fund of knowledge.