The science of God analyzes the constitutional position of God and His diverse energies. Material nature is called prakṛti, or the energy of the Lord in His different puruṣa incarnations (expansions) as described in the Sātvata-tantra:
viṣṇos tu trīṇi rūpāṇi
puruṣākhyāny atho viduḥ
ekaṁ tu mahataḥ sraṣṭṛ
dvitīyaṁ tv aṇḍa-saṁsthitam
tṛtīyaṁ sarva-bhūta-sthaṁ
tāni jñātvā vimucyate
"For material creation, Lord Kṛṣṇa's plenary expansion assumes three Viṣṇus. The first one, Mahā-Viṣṇu, creates the total material energy, known as the mahat-tattva. The second, Garbhodakaśāyī Viṣṇu, enters into all the universes to create diversities in each of them. The third, Kṣīrodakaśāyī Viṣṇu, is diffused as the all-pervading Supersoul in all the universes and is known as Paramātmā. He is present even within the atoms. Anyone who knows these three Viṣṇus can be liberated from material entanglement."
(Bhagavad-Gita-----7:4-----purport).

Kṛṣṇa first informs Arjuna that He is the soul of the entire cosmic manifestation by dint of His primary expansion. Before the material creation, the Supreme Lord, by His plenary expansion, accepts the puruṣa incarnations, and from Him everything begins. Therefore He is ātmā, the soul of the mahat-tattva, the universal elements. The total material energy is not the cause of the creation; actually Mahā-Viṣṇu enters into the mahat-tattva, the total material energy. He is the soul. When Mahā-Viṣṇu enters into the manifested universes, He again manifests Himself as the Supersoul in each and every entity. We have experience that the personal body of the living entity exists due to the presence of the spiritual spark. Without the existence of the spiritual spark, the body cannot develop. Similarly, the material manifestation cannot develop unless the Supreme Soul, Kṛṣṇa, enters. As stated in the Subāla Upaniṣad, prakṛty-ādi-sarva-bhūtāntar-yāmī sarva-śeṣī ca nārāyaṇaḥ: "The Supreme Personality of Godhead is existing as the Supersoul in all manifested universes." The three puruṣa-avatāras are described in Śrīmad-Bhāgavatam. They are also described in the Sātvata-tantra. Viṣṇos tu trīṇi rūpāṇi puruṣākhyāny atho viduḥ: the Supreme Personality of Godhead manifests three features—as Kāraṇodakaśāyī Viṣṇu, Garbhodakaśāyī Viṣṇu and Kṣīrodakaśāyī Viṣṇu—in this material manifestation. The Mahā-Viṣṇu, or Kāraṇodakaśāyī Viṣṇu, is described in the Brahma-saṁhitā (5.47). Yaḥ kāraṇārṇava-jale bhajati sma yoga-nidrām: the Supreme Lord, Kṛṣṇa, the cause of all causes, lies down in the cosmic ocean as Mahā-Viṣṇu. Therefore the Supreme Personality of Godhead is the beginning of this universe, the maintainer of the universal manifestations, and the end of all energy.
(Bhagavad-Gita-----10:20-----purport).

“Viṣṇu has three forms called puruṣas. The first, Mahā-Viṣṇu, is the creator of the total material energy [mahat], the second is Garbhodaśāyī, who is situated within each universe, and the third is Kṣīrodaśāyī, who lives in the heart of every living being. He who knows these three becomes liberated from the clutches of māyā.” This verse appears in the Laghu-bhāgavatāmṛta (Pūrva 2.9), where it has been quoted from the Sātvata-tantra.
(Sri Caitanya Caritamrta-----1:5:77-----translation and purport).

In the Mahābhārata, Śānti-parva, it is said that He who is Pradyumna is also Aniruddha. He is also the father of Brahmā. Thus Garbhodakaśāyī Viṣṇu and Kṣīrodakaśāyī Viṣṇu are identical plenary expansions of Pradyumna, the original Deity of Brahmā, who is born from the lotus flower. It is Pradyumna who gives Brahmā direction for cosmic management. A full description of Brahmā’s birth is given in Śrīmad-Bhāgavatam (3.8.15–16). Describing the features of the three puruṣas, the Laghu-bhāgavatāmṛta says that Garbhodakaśāyī Viṣṇu has a four-handed form, and when He Himself enters the hollow of the universe and lies down in the ocean of milk He is known as Kṣīrodakaśāyī Viṣṇu, who is the Supersoul of all living entities, including the demigods. In the Sātvata-tantra it is said that the third puruṣa incarnation, Kṣīrodakaśāyī Viṣṇu, is situated as the Supersoul in everyone’s heart. This Kṣīrodakaśāyī Viṣṇu is an expansion of Garbhodakaśāyī Viṣṇu for pastimes.
(Sri Caitanya Caritamrta-----1:5:93-----purport).

Kṛṣṇa first incarnates as the three puruṣa-avatāras, namely the Mahā-Viṣṇu or Kāraṇodakaśāyī avatāra, the Garbhodakaśāyī avatāra and the Kṣīrodakaśāyī avatāra. This is confirmed in the Sātvata-tantra. Kṛṣṇa's energies can also be divided into three: His energy of thinking feeling and acting. When He exhibits His thinking energy, He is the Supreme Lord; when He exhibits His feeling energy, He is Lord Vāsudeva; when He exhibits His acting energy, He is Saṅkarṣaṇa Balarāma. Without His thinking, feeling and acting, there would be no possibility of creation. Although there is no creation in the spiritual world—for there the planets are beginningless—there is creation in the material world. In either case, however, both the spiritual and material worlds are manifestations of the energy of acting, in which Kṛṣṇa acts in the form of Saṅkarṣaṇa and Balarāma.
(Teachings of Lord Caitanya).