Visnu-tattva means-

Srila Prabhupāda - "Sanātana means eternally they are divided. It is not that it has been divided by some means. Just like we keep water in big pot or small pot. That is not possible. They are big or small eternally. Viṣṇu-tattva, jīva-tattva. 

The jīva-tattva, they are small fragments. They are eternal. Viṣṇu-tattva. Viṣṇu-tattva means the Supreme Personality of Godhead. Viṣṇu-tattva is unlimitedly great eternally, sanātana.  And the jīva-tattva, they are infinitesimally smaller eternally. Not that it has been cut into small and big. No. 

So, this Māyāvādī theory cannot stand here if we accept the Bhagavad-gītā's statement. Nainaṁ chindanti śastrāṇi. It is not divided by some means. No. It is already divided. It is already divided. Neither the small piece of soul or the big piece of soul you can divide." (Lecture on BG, Ch 2.23-24 - London, Aug 27, 1973)

Srila Prabhupada - "So every viṣṇu-tattva is controller. There is no doubt. And they have got equal power. Not that Lordship Rāmacandra is less powerful than Kṛṣṇa. No. They have equal power. The example is described in the Brahma-saṁhitā. Dīpārcir eva hi daśāntaram abhyupetya [Bs. 5.46]. Just like one candle. You ignite another candle, you ignite another, another, another. But all these candles, they are equally powerful. 

Although you can say, "This is first candle, this is second candle, this is third candle..." Similarly, viṣṇu-tattva, everyone is equally powerful. Although Kṛṣṇa is first, Balarāma is second, Saṅkarṣaṇa is third, like that. But do not think They are less powerful. No. Viṣṇu-tattva means They are equally powerful. Svāṁśa. Rāmādi-mūrtiṣu kalā-niyamena tiṣṭhan [Bs. 5.39]. Kalā. Rāma is expansion of Viṣṇu, but it is not that Rāma is less powerful than Kṛṣṇa. Nobody is less powerful." (Lecture on SB, Canto 1.7.51-52 - Vrndavana, Oct 8, 1976)

Srila Prabhupada - "Anything about Nārāyaṇa, that is not of this material world. That is of the spiritual world. Therefore, Kṛṣṇa question and Kṛṣṇa answer, they are not material things. Therefore, if we always engage ourself in Kṛṣṇa question and Kṛṣṇa answer... śravaṇaṁ kīrtanaṁ viṣṇoḥ [SB 7.5.23]. Therefore it is called Viṣṇu. Not that any other śravaṇaṁ kīrtanam. Only Viṣṇu. 

Viṣṇu means viṣṇu-tattva. Rāmādi-mūrtiṣu kalā-niyamena tiṣṭhan. Viṣṇu-tattva means rāmādi-mūrti. Rāma, Nṛsiṁha, Varāha, Kṛṣṇa... There are so many. They are described. They are viṣṇu-tattva. Viṣṇu-tattva, jīva-tattva, śakti-tattva. There are different tattvas. So śravaṇaṁ kīrtanam. If you engage yourself in śravaṇaṁ kīrtanam, that should be for Viṣṇu, not for any other, anyone else." (Lecture on SB, Canto 2.1.3 - Delhi, Nov 6, 1973)

Srila Prabhupāda - "Actually, everyone, all the demigods, they have got their forms. But the difference is Viṣṇu, the form of Viṣṇu, is eternal; and the forms of demigods or the form, our forms... Just like we have got now some form. They're not eternal—temporary. 

We all sitting here, we have got different forms, but as soon as these forms will be changed, we shall accept another form—this form's gone forever. It will never come again. But Viṣṇu form, Lord Viṣṇu's form, viṣṇu-tattva. Viṣṇu-tattva means the forms of the original Lord, Kṛṣṇa. Kṛṣṇa is the original form. 

Kṛṣṇas tu bhagavān svayam [SB 1.3.28]. 

But He expands in different forms. The original form is Kṛṣṇa. Advaitam acyutam anādim ananta-rūpam [Bs. 5.33]. 

In the Brahma-saṁhitā it is said, Kṛṣṇa, advaita, one. There is no second, I mean to say, counterpart. But He expands. Advaitam acyutam. Acyuta. 

Acyuta means which does not fall down. 

Acyuta. Cyuta means "fall down." So God's another name is Acyuta, never falls down. 

Just like we living entities, we fall down. From spiritual world, we fall down. Because we have fallen down, therefore we have got this material body. But Kṛṣṇa, or God, never falls down." (Lecture on SB 2.3.22 - Los Angeles, June 19, 1972)

Srila Prabhupāda - "So one may be very educated, very good scholar in Vedic knowledge, but if he does not accept Viṣṇu, the Supreme Personality of Godhead, or Kṛṣṇa, the Supreme Personality of Godhead... Viṣṇu and Kṛṣṇa the same. Viṣṇu-tattva. 

Viṣṇu-tattva means the category of the Supreme Personality of Godhead. 

So durāśayā ye bahir-artha-māninaḥ. Out of false hopes, they are trying to become successful. That is not possible. Durāśayā. 

Such kind of hope is useless hope. It will never be... Moghāśā mogha-karmāṇaḥ. Leaving aside Viṣṇu and simply they are trying to become very highly learned, mogha-jñāna vicetasaḥ. So they are mogha, means their hopes will never be successful. They may go on." (Lecture on SB, Canto 5.5.29 - Vrndavana, Nov 16, 1976)

Srila Prabhupada - "There are two kinds of expansions of the Lord. One kind of expansion is called Viṣṇu-tattva. Viṣṇu-tattva means the expansion, they are as equal as the God Himself.  And there are expansions which are called the jīva-tattva, the living entities. This expansion of the living entities (jiva-souls), they are not equally powerful, but the expansion of Viṣṇu-tattva is equally powerful, as good as God Himself. 

So the incarnation... Incarnation of God means the expansion which is as good as God Himself. That is called incarnation. So this, I mean to, Hare Kṛṣṇa, Hare Kṛṣṇa, Kṛṣṇa Kṛṣṇa, Hare Hare/ Hare Rāma, Hare Rāma, Rāma Rāma, Hare Hare, is the expansion, incarnation, sound incarnation, of God. 

It is expansion and a plenary expansion, sound, sound representation... Not representation. God, present Himself in this form of sound." (Lecture on Maha-mantra - New York City, Sept 8, 1966)**