"There are many personalities possessing the qualities of Bhagavān, but Kṛṣṇa is the supreme because none can excel Him. He is the Supreme Person, and His body is eternal, full of knowledge and bliss. He is the primeval Lord Govinda and the cause of all causes." (Brahma-saṁhitā 5.1)
In the Bhāgavatam also there is a list of many incarnations of the Supreme Personality of Godhead, but Kṛṣṇa is described as the original Personality of Godhead, from whom many, many incarnations and Personalities of Godhead expand.
(Bhavagad-Gita----2:2----purport).

However, Kṛṣṇa can be known only by persons who are in Kṛṣṇa consciousness. Other transcendentalists may achieve impersonal Brahman realization, for this is easier than understanding Kṛṣṇa. Kṛṣṇa is the Supreme Person, but at the same time He is beyond the knowledge of Brahman and Paramātmā. The yogīs and jñānīs are confused in their attempts to understand Kṛṣṇa. Although the greatest of the impersonalists, Śrīpāda Śaṅkarācārya, has admitted in his Gītā commentary that Kṛṣṇa is the Supreme Personality of Godhead, his followers do not accept Kṛṣṇa as such, for it is very difficult to know Kṛṣṇa, even though one has transcendental realization of impersonal Brahman.
(Bhavagad-Gita----7:3----purport).

That the Personality of Godhead is the Supreme Absolute Truth is also the affirmation of the Brahma-saṁhitā: īśvaraḥ paramaḥ kṛṣṇaḥ sac-cid-ānanda-vigrahaḥ; that is, the Supreme Absolute Truth Personality of Godhead is Lord Kṛṣṇa, who is the primeval Lord, the reservoir of all pleasure, Govinda, and the eternal form of complete bliss and knowledge. These authorities leave no doubt that the Absolute Truth is the Supreme Person, the cause of all causes. The impersonalist, however, argues on the strength of the Vedic version given in the Śvetāśvatara Upaniṣad (3.10): tato yad uttarataraṁ tad arūpam anāmayam/ ya etad vidur amṛtās te bhavanti athetare duḥkham evāpiyanti. "In the material world Brahmā, the primeval living entity within the universe, is understood to be the supreme amongst the demigods, human beings and lower animals.
(Bhavagad-Gita----7:7----purport).

Kṛṣṇa knows every living entity because He is situated in every living being's heart as the Supersoul. But despite His presence in every living entity as Supersoul and His presence as the Supreme Personality of Godhead, the less intelligent, even if able to realize the impersonal Brahman, cannot realize Śrī Kṛṣṇa as the Supreme Person. Certainly the transcendental body of Śrī Kṛṣṇa is not perishable. He is just like the sun, and māyā is like a cloud. In the material world we can see that there is the sun and that there are clouds and different stars and planets. The clouds may cover all these in the sky temporarily, but this covering is only apparent to our limited vision. The sun, moon and stars are not actually covered. Similarly, māyā cannot cover the Supreme Lord. By His internal potency He is not manifest to the less intelligent class of men.
(Bhavagad-Gita----7:26----purport).

The mahātmā does not divert his attention to anything outside Kṛṣṇa, because he knows perfectly well that Kṛṣṇa is the original Supreme Person, the cause of all causes. There is no doubt about it. Such a mahātmā, or great soul, develops through association with other mahātmās, pure devotees. Pure devotees are not even attracted by Kṛṣṇa's other features, such as the four-armed Mahā-viṣṇu. They are simply attracted by the two-armed form of Kṛṣṇa. They are not attracted to other features of Kṛṣṇa, nor are they concerned with any form of a demigod or of a human being. They meditate only upon Kṛṣṇa in Kṛṣṇa consciousness. They are always engaged in the unswerving service of the Lord in Kṛṣṇa consciousness.
(Bhavagad-Gita----9:13----purport).

Such persons could not recognize Lord Śrī Kṛṣṇa even when He was present before them. Another difficulty is that those who depend more on their imperfect senses cannot realize Him as the Supreme Lord. Such persons are like the modern scientist. They want to know everything by their experimental knowledge. But it is not possible to know theSupreme Person by imperfect experimental knowledge. He is described herein as adhokṣaja, or beyond the range of experimental knowledge. All our senses are imperfect. We claim to observe everything and anything, but we must admit that we can observe things under certain material conditions only, which are also beyond our control. The Lord is beyond the observation of sense perception.
(Srimad Bhagavatam----1:8:19----purport).

Even the very question is so nice that it is the best subject matter for hearing. Simply by such questioning and hearing, one can achieve the highest perfectional stage of life. Because Lord Kṛṣṇa is the original Supreme Person, any question about Him is original and perfect. Lord Śrī Caitanya Mahāprabhu said that the highest perfection of life is to achieve the transcendental loving service of Kṛṣṇa. Because questions and answers about Kṛṣṇa elevate one to that transcendental position, the questions of Mahārāja Parīkṣit about Kṛṣṇa philosophy are greatly glorified.
(Srimad Bhagavatam----2:1:1----purport).

When a devotee is promoted to the spiritual world, Vaikuṇṭha, he receives four kinds of facilities. One of these is sālokya, living on the same planet as the Supreme Personality. The Supreme Person, in His different plenary expansions, lives on innumerable Vaikuṇṭha planets, and the chief planet is Kṛṣṇaloka. Just as within the material universe the chief planet is the sun, in the spiritual world the chief planet is Kṛṣṇaloka. From Kṛṣṇaloka, the bodily effulgence of Lord Kṛṣṇa is distributed not only to the spiritual world but to the material world as well; it is covered by matter, however, in the material world.
(Srimad Bhagavatam----3:29:13----purport).

The Supreme Personality of Godhead is originally the Supreme Person, and He expands Himself impersonally through His potency. As the Lord says in the Bhagavad-gītā (9.4):
mayā tatam idaṁ sarvaṁ jagad avyakta-mūrtinā
mat-sthāni sarva-bhūtāni na cāhaṁ teṣv avasthitaḥ
"By Me, in My unmanifested form, this entire universe is pervaded. All beings are in Me, but I am not in them." The potency of Kṛṣṇa that is spread everywhere is impersonal, just as the sunlight is the impersonal expansion of the sun globe and the sun-god. If we simply take one side of the Supreme Personality of Godhead—His impersonal effulgence—that one side does not fully explain the Absolute Truth.
(Sri Caitanya Caritamrta----2:25:33----purport).

One has to approach the Supreme Personality of Godhead, Kṛṣṇa, as it is stated in Bhagavad-gītā: "After many, many births, one approaches the Supreme Person, Kṛṣṇa, and surrenders unto Him, knowing that He is everything." Also in Bhagavad-gītā, the Lord says, bhoktāraṁ yajña-tapasām: (B.G.5:29) "For anyone who is undergoing rigid austerity or for anyone performing different kinds of sacrifices, the beneficiary is the Supreme Personality of Godhead." He is the proprietor of all planets, and He is the friend of every living soul.
(Srimad Bhagavatam----3:32:34-36----purport).

He is present with His form, qualities, name, entourage and paraphernalia. Therefore, Kṛṣṇa is not impersonal. The original cause of everything is neither void nor impersonal but is theSupreme Person. Demons may say that this material creation is anīśvara, without a controller or God, but such arguments ultimately cannot stand.
The example given by the Māyāvādī philosophers that inanimate matter like nails and hair comes from the living body is not a very sound argument. Nails and hair are undoubtedly inanimate, but they come not from the animate living being but from the inanimate material body. Similarly, the argument that the scorpion comes from cow dung, meaning that a living entity comes from matter, is also unsound. The scorpion which comes out of the cow dung is certainly a living entity, but the living entity does not come out of the cow dung.
(Krsna Book).

He is the supreme potency of all material senses or sense organs. He is omnipotent, and He is the supreme performer of everything. Therefore He is worshipable by everyone. Unto thatSupreme Person do I offer my respectful obeisances.”
Kṛṣṇa Himself declares in the Bhagavad-gītā that because He is transcendental to all sentient and insentient beings He is known as Puruṣottama, which means the Supreme Personality. (Puruṣa means "person," and uttama means "supreme" or "transcendental.") In another place the Lord says that as the air is situated in the all-pervading sky, everyone is situated in Him, and everyone is acting under His direction.
(Krsna Book).

The Supreme Personality of Godhead is sac-cid-ānanda-vigraha (Bs. 5.1). Realization of impersonal Brahman is realization of His sat feature, or His aspect of eternity, and Paramātmā realization is realization of His sat and cit features, His aspects of eternity and knowledge. But realization of the Personality of Godhead is realization of all the transcendental features—sat, cit and ānanda, bliss. When one realizes the Supreme Person, he realizes these aspects of the Absolute Truth in their completeness. Vigraha means "form." Thus the Complete Whole is not formless. If He were formless, or if He were less than His creation in any other way, He could not be complete. The Complete Whole must contain everything both within and beyond our experience; otherwise He cannot be complete.
(Sri Isopanishad).

Before hearing the Bhagavad-gītā, Arjuna was disturbed by the material whirlpool, by his affection for his family, society and community. Thus Arjuna wanted to become a philanthropic, nonviolent man of the world. But when he became budha by hearing the Vedic knowledge of the Bhagavad-gītā from the Supreme Person, he changed his decision and became a worshiper of Lord Śrī Kṛṣṇa, who had Himself arranged the Battle of Kurukṣetra. Arjuna worshiped the Lord by fighting with his so-called relatives, and in this way he became a pure devotee of the Lord. Such accomplishments are possible only when one worships the real Kṛṣṇa and not some fabricated "Kṛṣṇa" invented by foolish men who are without knowledge of the intricacies of the science of Kṛṣṇa described in the Bhagavad-gītā and Śrīmad-Bhāgavatam.
(Sri Isopanishad).

The predominating Supreme Person residing within the spiritual nature is Lord Śrī Kṛṣṇa. As confirmed in the Bhagavad-gītā (8.22), He can be approached only by unalloyed devotional service and not by the processes of jñāna (philosophy), yoga (mysticism) or karma (fruitive work). The karmīs, or fruitive workers, can elevate themselves to the Svargaloka planets, which include the sun and the moon. Jñānīs and yogīs can attain still higher planets, such as Maharloka, Tapoloka and Brahmaloka, and when they become still more qualified through devotional service they can enter into the spiritual nature, either the illuminating cosmic atmosphere of the spiritual sky (Brahman) or the Vaikuṇṭha planets, according to their qualification. It is certain, however, that no one can enter into the spiritual Vaikuṇṭha planets without being trained in devotional service.
(Sri Isopanishad).

The Lord is the eternal Supreme Person, and therefore His name, form, qualities, pastimes, and so on are all eternal. The Sanskrit word puruṣa means "enjoyer." An enjoyer can never be a formless, impersonal, impotent being. Certainly Lord Kṛṣṇa is without material qualities, yet He is the enjoyer and possessor of all spiritual qualities.
(Renunciation Through Wisdom).

If a highly placed servant in the king's court is mistakenly honored as the king, that does not mean the king becomes the servant and vice versa. Similarly, Lord Kṛṣṇa is the only Supreme Person, and everyone else is His servant. The Brahma-saṁhitā clearly explains the relationship between Lord Kṛṣṇa and the demigods. There are numerous proofs that beings who are in the category of viṣṇu-tattva-supreme personalities on the level of Lord Viṣṇu—are the highest absolute beings. The Śrīmad-Bhāgavatam confirms this truth by proclaiming that of all kinds of worship, worship of Lord Viṣṇu, or Kṛṣṇa, is the most elevated.
(Renunciation Through Wisdom).

Those who cannot understand this truth remain far from the science of devotional service, while those who do understand it are strengthened in their devotional life. Lord Kṛṣṇa is the Supreme Personality of Godhead, the supreme male. So, when the supreme male is present, automatically material nature, his female counterpart, is there to serve Him. Those who falsely pose as the Supreme Person claim to have the material nature at their disposal and conclude that nature is no longer at Lord Kṛṣṇa's beck and call. Naturally this is absurd, and only fools will make such a claim.
(Renunciation Through Wisdom).

In pure devotional service one simply serves the Supreme Personality of Godhead as a matter of duty, without reason and without being impeded by material conditions. That is called śuddha-sattva, or vasudeva, because in that stage the Supreme Person, Kṛṣṇa, is revealed in the heart of the devotee. Śrīla Jīva Gosvāmī has very nicely described this vasudeva, or śuddha-sattva, in his Bhagavat-sandarbha. He explains that aṣṭottara-śata (108) is added to the name of the spiritual master to indicate one who is situated in śuddha-sattva, or in the transcendental state of vasudeva. The word vasudeva is also used for other purposes. For example, vasudeva also means one who is everywhere, or all-pervading. The sun is also called vasudeva-śabditam. The word vasudeva may be utilized for different purposes, but whatever purpose we adopt, Vāsudeva means the all-pervading or localized Supreme Personality of Godhead. In Bhagavad-gītā (7.19) it is also stated, vāsudevaḥ sarvam iti. Factual realization is to understand Vāsudeva, the Supreme Personality of Godhead, and surrender unto Him. Vasudeva is the ground wherein Vāsudeva, the Supreme Personality of Godhead, is revealed. When one is free from the contamination of material nature and is situated in pure Kṛṣṇa consciousness, or in the vasudeva state, Vāsudeva, the Supreme Person, is revealed.
(Srimad Bhagavatam----4:3:23----purport).

The conception of "I" and "you," ahaṁ tvam, as separate from each other, is due to our forgetfulness of our eternal relationship with the Supreme Personality of Godhead. The Supreme Person, Kṛṣṇa, is the central point, and all of us are His parts and parcels, just as hands and legs are parts and parcels of the whole body. When we actually come to this understanding of being eternally related to the Supreme Lord, this distinction, which is based on the bodily concept of life, cannot exist. The same example can be cited herewith: the hand is the hand, and the leg is the leg, but when both of them engage in the service of the whole body, there is no such distinction as "hands" and "legs," for all of them belong to the whole body, and all the parts working together constitute the whole body.
(Srimad Bhagavatam----4:12:4----purport).

Oṁkāra (praṇava) is the symbolic sound representation of the Supreme Personality of Godhead. Oṁ tat sad iti nirdeśo brahmaṇas tri-vidhaḥ smṛtaḥ: the three words oṁ tat sat immediately invoke the Supreme Person. Therefore Kṛṣṇa says that He is oṁkāra in all the Vedic mantras (praṇavaḥ sarva-vedeṣu). The Vedic mantras are pronounced beginning with oṁkāra to indicate immediately the Supreme Personality of Godhead. Śrīmad-Bhāgavatam, for example, begins with the words oṁ namo bhagavate vāsudevāya. There is no difference between the Supreme Personality of Godhead, Vāsudeva, and oṁkāra (praṇava).
(Srimad Bhagavatam----8:3:2----purport).

"The Supreme is blissful, with no tinge of unhappiness. Although He is the oldest, He never ages, and although one, He is experienced in different forms." Sarve nityāḥ śāśvatāś ca dehās tasya parātmanaḥ: "All the forms of that Supreme Person are eternal." (Mahā-varāha Purāṇa) The Supreme Person has a form, with hands and legs and other personal features, but His hands and legs are not material. Bhaktas know that the form of Kṛṣṇa, or Brahman, is not at all material. Rather, Brahman has a transcendental form, and when one is absorbed in it, being fully developed in bhakti, one can understand Him (premāñjana-cchurita-bhakti-vilocanena (Bs. 5.38)). The Māyāvādīs, however, cannot understand this transcendental form, for they think that it is material.
(Srimad Bhagavatam----10:13:54----purport).

The word parātma-niṣṭhā means being a devotee of Lord Kṛṣṇa. Parātmā, the Supreme Person, is Kṛṣṇa. Īśvaraḥ paramaḥ kṛṣṇaḥ sac-cid-ānanda-vigrahaḥ (Bs. 5.1). Those who are completely dedicated to the lotus feet of Kṛṣṇa in service are actually sannyāsīs. As a matter of formality, the devotee accepts the sannyāsa dress as previous ācāryas did. He also accepts the three daṇḍas. Later Viṣṇu Svāmī considered that accepting the dress of a tri-daṇḍī was parātma-niṣṭhā. Therefore sincere devotees add another daṇḍa, the jīva-daṇḍa, to the three existing daṇḍas. The Vaiṣṇava sannyāsī is known as a tridaṇḍi-sannyāsī.
(Sri Caitanya Caritamrta----2:3:6----purport).

When Kṛṣṇa says aham, He says "I am," which means "I," the person. He adds the word eva, which is used for conclusive verification. Thus by studying Vedānta philosophy one must come to know the Supreme Person. Whoever describes Vedic knowledge as impersonal is a demon. One becomes successful in life by worshiping the form of the Lord. The Māyāvādī sannyāsīs deny the form of the Lord, which delivers all fallen souls. Indeed, the Māyāvādī demons try to cut this form to pieces.
(Sri Caitanya Caritamrta----2:17:104----purport).

The Lord is the Supersoul, spiritual master and worshipable Deity of all conditioned souls. Not only is Kṛṣṇa the supreme worshipful Deity for all living entities, but He is also the guru, or caittya-guru, the Supersoul, who always gives the living entity good counsel. Unfortunately the living entity neglects the Supreme Person's instructions. He thus identifies with the material energy and is consequently overpowered by a kind of fear resulting from accepting himself as the material body and considering paraphernalia related to the material body to be his property. All types of fruitive results actually come from the spirit soul, but because he has forgotten his real duty, he is embarrassed by many material consequences such as fear and attachment. The only remedy is to revert to the service of the Lord and thus be saved from material nature's unwanted harassment.

(Sri Caitanya Caritamrta----2:20:119----purport).