Mahā-viṣṇu, enters. He lies within the Causal Ocean and breathes out innumerable universes, and into each universe the Lord again enters as Garbhodakaśāyī Viṣṇu. Each universe is in that way created. He still further manifests Himself as Kṣīrodakaśāyī Viṣṇu, and that Viṣṇu enters into everything—even into the minute atom. This fact is explained here. He enters into everything.
Now, as far as the living entities are concerned, they are impregnated into this material nature, and as a result of their past deeds they take different positions. Thus the activities of this material world begin. The activities of the different species of living beings are begun from the very moment of the creation. It is not that all is evolved.
(Bhagavad-Gita----9:8----purport).

His plenary parts are viṣṇu-tattva, or the Lordship of Godhead. From Śrī Kṛṣṇa, the next manifestation is Baladeva. From Baladeva is Saṅkarṣaṇa, from Saṅkarṣaṇa is Nārāyaṇa, from Nārāyaṇa there is the second Saṅkarṣaṇa, and from this Saṅkarṣaṇa the Viṣṇu puruṣa-avatāras. The Viṣṇu or the Deity of the quality of goodness in the material world is the puruṣa-avatāra known as Kṣīrodakaśāyī Viṣṇu or Paramātmā. Brahmā is the deity of rajas (passion), and Śiva of ignorance. They are the three departmental heads of the three qualities of this material world. The creation is made possible by Brahma's quality of passion and his endeavor, it is maintained by the goodness of Viṣṇu, and when it requires to be destroyed, Lord Śiva does it by the tāṇḍava-nṛtya. The materialists and the foolish human beings worship Brahmā and Śiva respectively.
(Srimad Bhagavatam----1:2:23----purport).

This Brahmā is in charge of further creations in the universe, secondarily reflected by the potency of the Omnipotent. Within the halo of the universe there is a transcendental planet known as Śvetadvīpa, which is the abode of the Kṣīrodakaśāyī Viṣṇu, the Paramātmā feature of the Supreme Lord. Whenever there is trouble in the universe that cannot be solved by the administrative demigods, they approach Brahmājī for a solution, and if it is not to be solved even by Brahmājī, then Brahmājī consults and prays to the Kṣīrodakaśāyī Viṣṇu for an incarnation and solution to the problems. Such a problem arose when Kaṁsa and others were ruling over the earth and the earth became too much overburdened by the misdeeds of the asuras. Brahmājī, along with other demigods, prayed at the shore of the Kṣīrodaka Ocean, and they were advised of the descent of Kṛṣṇa as the son of Vasudeva and Devakī. So some people say that the Lord appeared because of the prayers of Brahmājī.
(Srimad Bhagavatam----1:8:34----purport).

This ocean of milk and the Śvetadvīpa planet are the replica of Vaikuṇṭhaloka within the universe. Neither Brahmājī nor the demigods like Indra can enter into this island of Śvetadvīpa, but they can stand on the shore of the ocean of milk and transmit their message to Lord Viṣṇu, known as Kṣīrodakaśāyī Viṣṇu. Therefore, the Lord is rarely seen by them, but the inhabitants of Dvārakā, because of their being pure devotees without any tinge of the material contamination of fruitive activities and empiric philosophical speculation, can see Him face to face by the grace of the Lord. This is the original state of the living entities and can be attained by reviving our natural and constitutional state of life, which is discovered by devotional service only.
(Srimad Bhagavatam----1:11:8----purport).

This material world is a manifestation of the three modes goodness, passion and ignorance, and the Supreme Lord, for the creation, maintenance and destruction of the material world, accepts three predominating forms as Brahmā, Viṣṇu and Śaṅkara (Śiva). As Viṣṇu He enters into every body materially created. As Garbhodakaśāyī Viṣṇu He enters into every universe, and as Kṣīrodakaśāyī Viṣṇu He enters the body of every living being. Lord Śrī Kṛṣṇa, being the origin of all viṣṇu-tattvas, is addressed here as paraḥ pumān, or Puruṣottama, as described in the Bhagavad-gītā (15.18). He is the complete whole. The puruṣāvatāras are therefore His plenary expansions. Bhakti-yoga is the only process by which one can become competent to know Him. Because the empiric philosophers and mystic yogīs cannot conceive of the Personality of Godhead, He is called anupalakṣya-vartmane, the Lord of the inconceivable way, or bhakti-yoga.
(Srimad Bhagavatam----2:4:12----purport).

The ingredients for creation and the subordinate creator, Brahmā, are first created by Lord Viṣṇu in His first and second incarnations. The first puruṣa incarnation is Mahā-viṣṇu, and the second puruṣa incarnation is the Garbhodakaśāyī Viṣṇu, from whom Brahmā is created. The third puruṣa avatāra is the Kṣīrodakaśāyī Viṣṇu, who lives as the Supersoul of everything in the universe and maintains the creation generated by Brahmā. Śiva is one of the many sons of Brahmā, and he annihilates the creation. Therefore the original creator of the universe is Viṣṇu, and He is also the maintainer of the created beings by His causeless mercy. As such, it is the duty of all conditioned souls to acknowledge the victory of the Lord and thus become pure devotees and live peacefully in this world, where miseries and dangers are always in existence. The conditioned souls, who take this material creation as the place for satisfaction of the senses and thus are illusioned by the external energy of Viṣṇu, remain again to be subjected to the laws of material nature, creation and destruction.
(Srimad Bhagavatam----2:10:4----purport).

Lord Kṛṣṇa is the original Personality of Godhead from whom the three creative incarnations, namely the puruṣa-avatāras—Kāraṇārṇavaśāyī Viṣṇu, Garbhodakaśāyī Viṣṇu and Kṣīrodakaśāyī Viṣṇu—expand. The whole material creation is conducted by the three puruṣas in successive stages under the external energy of the Lord, and thus material nature is controlled by Him. Thinking material nature to be independent is like seeking milk from the nipplelike bags on the neck of a goat. The Lord is independent and desireless. He does not create the material world for His own satisfaction as we create our household affairs to fulfill our material desires. Actually the material world is created for the illusory enjoyment of the conditioned souls, who have been against the transcendental service of the Lord since time immemorial. But the material universes are full in themselves. There is no scarcity for maintenance in the material world.
(Srimad Bhagavatam----3:5:5----purport).

The three deities Brahmā, Viṣṇu and Maheśvara (Śiva), the executive heads of the three modes of material nature (passion, goodness and ignorance), are all generated from Garbhodakaśāyī Viṣṇu, who is described herein by Brahmā. From the Kṣīrodakaśāyī Viṣṇu, many Viṣṇu incarnations expand at different ages in the duration of the cosmic manifestation. They are expanded only for the transcendental happiness of the pure devotees. The incarnations of Viṣṇu, who appear at different ages and times, are never to be compared to the conditioned souls. The viṣṇu-tattvas are not to be compared to deities like Brahmā and Śiva, nor are they on the same level. Anyone who compares them is called a pāṣaṇḍī, or infidel. Tamasaḥ, mentioned herein, is the material nature, and the spiritual nature has a completely separate existence from tamaḥ.
(Srimad Bhagavatam----3:9:2----purport).

When He is realized in His impersonal form He is called the Supreme Brahman, when realized as the Paramātmā He is called antaryāmī, and when He expands Himself in different forms for material creation He is called Kṣīrodakaśāyī Viṣṇu, Garbhodakaśāyī Viṣṇu and Kāraṇodakaśāyī Viṣṇu. When He is realized as Vāsudeva, Saṅkarṣaṇa, Pradyumna and Aniruddha—the Caturvyūha, who are beyond the three forms of Viṣṇu—He is the Vaikuṇṭha Nārāyaṇa. Above realization of Nārāyaṇa is realization of Baladeva, and above that is realization of Kṛṣṇa. All these realizations are possible when one engages fully in devotional service. The covered core of one's heart is then completely open to receiving an understanding of the Supreme Personality of Godhead in His various forms.
(Srimad Bhagavatam----6:9:33----purport).

Oṁ namo bhagavate vāsudevāya. Vāsudeva, who is an expansion of Nārāyaṇa, expands Himself as Pradyumna, Aniruddha and Saṅkarṣaṇa. From Saṅkarṣaṇa comes a second Nārāyaṇa expansion, and from this Nārāyaṇa come further expansions of Vāsudeva, Pradyumna, Saṅkarṣaṇa and Aniruddha. The Saṅkarṣaṇa in this group is the original cause of the three puruṣas, namely Kāraṇodakaśāyī Viṣṇu, Garbhodakaśāyī Viṣṇu and Kṣīrodakaśāyī Viṣṇu. Kṣīrodakaśāyī Viṣṇu is situated in every universe in a special planet called Śvetadvīpa. This is confirmed in the Brahma-saṁhitā: aṇḍāntara-stha. The word aṇḍa means this universe. Within this universe is a planet called Śvetadvīpa, where Kṣīrodakaśāyī Viṣṇu is situated. From Him come all the incarnations within this universe.
(Srimad Bhagavatam----6:16:18-19----purport).

From Kṛṣṇa, or Govinda, comes Balarāma; from Balarāma comes Saṅkarṣaṇa; from Saṅkarṣaṇa, Nārāyaṇa; from Nārāyaṇa, the second Saṅkarṣaṇa; from the second Saṅkarṣaṇa, Mahā-viṣṇu; from Mahā-viṣṇu, Garbhodakaśāyī Viṣṇu; and from Garbhodakaśāyī Viṣṇu, Kṣīrodakaśāyī Viṣṇu. Kṣīrodakaśāyī Viṣṇu controls every universe. This gives an idea of the meaning of ananta, unlimited. What is to be said of the unlimited potency and existence of the Lord? This verse describes the coverings of the universe (saptabhir daśa-guṇottarair aṇḍa-kośaḥ). The first covering is earth, the second is water, the third is fire, the fourth is air, the fifth is sky, the sixth is the total material energy, and the seventh is the false ego. Beginning with the covering of earth, each covering is ten times greater than the previous one. Thus we can only imagine how great each universe is, and there are many millions of universes. As confirmed by the Lord Himself in Bhagavad-gītā (10.42):
(Srimad Bhagavatam----6:16:37----purport).

Thus when all these became assembled by force of the energy of the Supreme Personality of Godhead, this universe certainly came into being by accepting both the primary and secondary causes of creation.
In this verse it is clearly mentioned that the Supreme Personality of Godhead exerts His different energies in the creation; it is not that He Himself is transformed into material creations. He expands Himself by His different energies, as well as by His plenary portions. In a corner of the spiritual sky of brahmajyoti a spiritual cloud sometimes appears, and the covered portion is called the mahat-tattva. The Lord then, by His plenary portion as Mahā-Viṣṇu, lies down within the water of the mahat-tattva, and the water is called the Causal Ocean (Kāraṇa-jala). While Mahā-Viṣṇu sleeps within the Causal Ocean, innumerable universes are generated along with His breathing. These universes are floating, and they are scattered all over the Causal Ocean. They stay only during the breathing period of Mahā-Viṣṇu. In each and every universal globe, the same Mahā-Viṣṇu enters again as Garbhodakaśāyī Viṣṇu and lies there on the serpentlike Śeṣa incarnation. From His navel sprouts a lotus stem, and on the lotus, Brahmā, the lord of the universe, is born. Brahmā creates all forms of living beings of different shapes in terms of different desires within the universe. He also creates the sun, moon and other demigods.
Therefore the chief engineer of the material creation is the Lord Himself, as confirmed in the Bhagavad-gītā (9.10). It is He only who directs the material nature to produce all sorts of moving and nonmoving creations.
There are two modes of material creation: the creation of the collective universes, as stated above, done by the Mahā-Viṣṇu, and the creation of the single universe. Both are done by the Lord, and thus the universal shape, as we can see, takes place.
(Srimad Bhagavatam----2:5:33---- translation and purport).

When Brahmā goes to sleep in his nighttime, the three planetary systems below Brahmaloka are all submerged in the water of devastation. In his sleeping condition, Brahmā dreams about the Garbhodakaśāyī Viṣṇu and takes instruction from the Lord for the rehabilitation of the devastated area of space.
(Srimad Bhagavatam----3:11:22----purport).

Therefore, the conclusion is that the puruṣa-avatāra is manifested in three features—first the Kāraṇodakaśāyī who creates aggregate material ingredients in the mahat-tattva, second the Garbhodakaśāyī who enters in each and every universe, and third the Kṣīrodakaśāyī Viṣṇu who is the Paramātmā of every material object, organic or inorganic. One who knows these plenary features of the Personality of Godhead knows Godhead properly, and thus the knower becomes freed from the material conditions of birth, death, old age and disease, as it is confirmed in Bhagavad-gītā, In this śloka the subject matter of Mahā-Viṣṇu is summarized. The Mahā-Viṣṇu lies down in some part of the spiritual sky by His own free will. Thus He lies on the ocean of kāraṇa, from where He glances over His material nature, and the mahat-tattva is at once created. Thus electrified by the power of the Lord, the material nature at once creates innumerable universes, just as in due course a tree decorates itself with innumerable grown fruits. The seed of the tree is sown by the cultivator, and the tree or creeper in due course becomes manifested with so many fruits. Nothing can take place without a cause. The Kāraṇa Ocean is therefore called the Causal Ocean. Kāraṇa means "causal." We should not foolishly accept the atheistic theory of creation. The description of the atheists is given in the Bhagavad-gītā. The atheist does not believe in the creator, but he cannot give a good theory to explain the creation. Material nature has no power to create without the power of the puruṣa, just as a prakṛti, or woman, cannot produce a child without the connection of a puruṣa, or man. The puruṣa impregnates, and the prakṛti delivers. We should not expect milk from the fleshy bags on the neck of a goat, although they look like breastly nipples. Similarly, we should not expect any creative power from the material ingredients; we must believe in the power of the puruṣa, who impregnates prakṛti, or nature. Because the Lord wished to lie down in meditation, the material energy created innumerable universes at once, in each of them the Lord lay down, and thus all the planets and the different paraphernalia were created at once by the will of the Lord. The Lord has unlimited potencies, and thus He can act as He likes by perfect planning, although personally He has nothing to do. No one is greater than or equal to Him. That is the verdict of the Vedas.
(Srimad Bhagavatam----1:3:2----purport).