In the Brahma-saṁhitā it is said:
- yaḥ kāraṇārṇava-jale bhajati sma yoga-
- nidrām ananta-jagad-aṇḍa-saroma-kūpaḥ
- sa viṣṇur mahān sa iha yasya kalā-viśeṣo
- govindam ādi-puruṣaṁ tam ahaṁ bhajāmi
- (Bs. 5.47)
"I worship Govinda, the primeval Lord." Govindam ādi-puruṣam. Puruṣam means the Lord is male, enjoyer; Adi, the original. Govindam ādi-puruṣaṁ tam ahaṁ bhajāmi. And who is that Govinda? Whose only one plenary portion is Mahā-Viṣṇu. And what is the function of Mahā-Viṣṇu? Yasyaika-niśvasita-kālam athāvalambya jīvanti loma-vilajā jagad-aṇḍa-nāthāḥ (Bs. 5.48).
In every universe there is a chief living entity who is known as Brahmā. Brahmā is the original person in each universe. So the life of Brahmā or the life of an universe is existing only on the breathing period of Mahā-Viṣṇu. Mahā-Viṣṇu is lying on the Causal Ocean, and while He is exhaling, millions of universes are coming as bubbles, and they are developing again. And when He is inhaling, millions of universes are going within Him.
So that is the position of this material world. It is coming out and again going. Bhūtvā bhūtvā pralīyate (BG 8.19).
In the Bhagavad-gītā also it is said that these material universes are being created at a certain period and again become annihilated. Now this creation and annihilation is depending on the exhaling and inhaling of Mahā-Viṣṇu. Just imagine what is the caliber of that Mahā-Viṣṇu.
But that Mahā-Viṣṇu is said here: yasyaika-niśvasita-kālam athāvalambya jīvanti loma-vilajā jagad-aṇḍa-nāthāḥ viṣṇur mahān sa iha yasya kalā-viśeṣaḥ (Bs. 5.48). This Mahā-Viṣṇu is plenary portion of the plenary portion of Kṛṣṇa. Kṛṣṇa is the original, govindam ādi-puruṣaṁ tam ahaṁ bhajāmi. So this Mahā-Viṣṇu again enters into each universe as Garbhodakaśāyī Viṣṇu. And from Garbhodakaśāyī Viṣṇu there is Kṣīrodakaśāyī Viṣṇu. That Kṣīrodakaśāyī Viṣṇu is entering in the heart of every living entity. In this way, the Viṣṇu manifestation is all over the creation.
So the yogī's concentration of mind on this Viṣṇu form, that is explained here. That Viṣṇu, who is all-pervading, who is īśvaraḥ sarva-bhūtānāṁ hṛd-deśe 'rjuna tiṣṭhati (BG 18.61).
In the Bhagavad-gītā you'll find that Mahā-Viṣṇu . . . that Kṣīrodakaśāyī Viṣṇu is sitting in everyone's heart. Now yogī has to find out where He is sitting and concentrate this mind there. That is the yoga process.