Why is Krishna "The Supreme Personality of Godhead"?

 Bhagavad-gita, 10.12

You (Krishna) are the Supreme Personality of Godhead, the ultimate abode, the purest, the Absolute Truth. You are the eternal, transcendental, original person, the unborn, the greatest. All the great sages such as Narada, Asita, Devala and Vyasa confirm this truth about You, and now You Yourself are declaring it to me.

Brahma-samhita, 5.1

Krishna, who is known as Govinda is the Supreme Godhead. He has an eternal blissful spiritual body. He is the origin of all. He has no other origin and He is the prime cause of all causes.

Srimad-Bhagavatam, 1.1.1:

O my Lord, Sri Krishna, son of Vasudeva, O all-pervading Personality of Godhead, I offer my respectful obeisances unto You. I meditate upon Lord Sri Krishna because He is the Absolute Truth and the primeval cause of all causes of the creation, sustenance and destruction of the manifested universes. He is directly and indirectly conscious of all manifestations, and He is independent because there is no other cause beyond Him. It is He only who first imparted the Vedic knowledge unto the heart of Brahmaji, the original living being. By Him even the great sages and demigods are placed into illusion, as one is bewildered by the illusory representations of water seen in fire, or land seen on water. Only because of Him do the material universes, temporarily manifested by the reactions of the three modes of nature, appear factual, although they are unreal. I therefore meditate upon Him, Lord Sri Krishna, who is eternally existent in the transcendental abode, which is forever free from the illusory representations of the material world. I meditate upon Him, for He is the Absolute Truth.

Bhagavad-gita, 5.29

A person in full consciousness of Me, knowing Me to be the ultimate beneficiary of all sacrifices and austerities, the Supreme Lord of all planets and demigods, and the benefactor and well-wisher of all living entities, attains peace from the pangs of material miseries.

Chaitanya Charitamrita, Adi-lila 5.142

Lord Krishna alone is the supreme controller, and all others are His servants. They dance as He makes them do so.

Chaitanya Charitamrita, Adi-lila 7.7 

Krishna, the reservoir of all pleasure, is the Supreme Personality of Godhead Himself, the supreme controller. No one is greater than or equal to Sri Krishna, yet He appears as the son of Maharaja Nanda.

Srimad-Bhagavatam, 10.68.37, as well as Chaitanya Charitamrita, Madhya-lila, 20.306

What is the value of a throne to Lord Krishna? The masters of the various planetary systems accept the dust of His lotus feet on their crowned heads. That dust makes the holy places sacred, and even Lord Brahma, Lord Shiva, Laksmi and I Myself, who are all portions of His plenary portion, eternally carry that dust on our heads.

Bhagavad-gita, 7.7

O conqueror of wealth, there is no truth superior to Me. Everything rests upon Me, as pearls are strung on a thread.

Bhagavad-gita, 10.12-13, Purport

In the Kena Upanishad it is stated that the Supreme Brahman is the rest for everything, and Krishna has already explained that everything is resting on Him. The Mundaka Upanishad confirms that the Supreme Lord, in whom everything is resting, can be realized only by those who engage constantly in thinking of Him.

Atharva Veda (Gopala-tapani Upanishad 1.24)

yo brahmanam vidadhati purvam yo vai vedams ca gapayati sma krsnah: "It was Krishna who in the beginning instructed Brahma in Vedic knowledge and who disseminated Vedic knowledge in the past.

Narayana Upanishad (1)

atha puruso ha vai narayano 'kamayata prajah srjeyeti: 'Then the Supreme Personality Narayana desired to create living entities.' The Upanisad continues; narayanad brahma jayate, narayanad prajapatih prajayate, narayanad indro jayate, narayanad astau vasavo jayante, narayanad ekadasa rudra jayante, narayanad dvadasadityah: 'From Narayana, Brahma is born, and from Narayana the patriarchs are also born. From Narayana, Indra is born, from Narayana the eight Vasus are born, from Narayana the eleven Rudras are born, from Narayana the twelve Adityas are born.' This Narayana is an expansion of Krishna.

Narayana Upanishad (4)

brahmanyo devaki-putrah: 'The son of Devaki, Krishna, is the Supreme Personality.' Then it is said, eko vai narayana asin na brahma na isano napo nagni-somau neme dyav-aprthivi na naksatrani na suryah: 'In the beginning of the creation there was only the Supreme Personality Narayana. There was no Brahma, no Siva, no water, no fire, no moon, no heaven and earth, no stars in the sky, no sun.'

Mahabharata, Moksha-dharma

prajapatim ca rudram capy
aham eva srjami vai
tau hi mam na vijanito
mama maya-vimohitau

'The patriarchs, Siva and others are created by Me, though they do not know that they are created by Me because they are deluded by My illusory energy.'

Varaha Purana

narayanah paro devas
 tasmaj jatas caturmukhahtasmad rudro 'bhavad devahsa ca sarva-jnatam gatah

'Narayana is the Supreme Personality of Godhead, and from Him Brahma was born, from whom Siva was born.'

Bhagavad-gita, 10.8

I am the source of all spiritual and material worlds. Everything emanates from Me. The wise who perfectly know this engage in My devotional service and worship Me with all their hearts.

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