Srimad Bhagavatam Canto 05, Chapter 12, Text 11

SB 5.12.11

jñanam visuddham paramartham ekam
 anantaram tv abahir brahma satyam
pratyak prasantam bhagavac-chabda-samjñam
 yad vasudevam kavayo vadanti
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada: 
What, then, is the ultimate truth? The answer is that nondual knowledge is the ultimate truth. It is devoid of the contamination of material qualities. It gives us liberation. It is the one without a second, all-pervading and beyond imagination. The first realization of that knowledge is Brahman. Then Paramatma, the Supersoul, is realized by the yogis who try to see Him without grievance. This is the second stage of realization. Finally, full realization of the same supreme knowledge is realized in the Supreme Person. All learned scholars describe the Supreme Person as Vasudeva, the cause of Brahman, Paramatma and others.
Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada: 
In Caitanya-caritamrta it is said: yad advaitam brahmopanisadi tad apy asya tanu-bha. The impersonal Brahman effulgence of the Absolute Truth consists of the bodily rays of the Supreme Personality of Godhead. Ya atmantaryami purusa iti so ’syamsa-vibhavah. What is known as atma and antaryami, the Supersoul, is but an expansion of the Supreme Personality of Godhead. Sad-aisvaryaih purno ya iha bhagavan sa svayam ayam. What is described as the Supreme Personality of Godhead, complete with all six opulences, is Vasudeva, and Sri Caitanya Mahaprabhu is nondifferent from Him. Great learned scholars and philosophers accept this after many, many births. Vasudevah sarvam iti sa mahatma sudurlabhah (Bg. 7.19). The wise man can understand that ultimately Vasudeva, Krsna, is the cause of Brahman, and Paramatma, the Supersoul. Thus Vasudeva is sarva-karana-karanam, the cause of all causes. This is confirmed in Srimad-Bhagavatam. The real tattva, Absolute Truth, is Bhagavan, but due to incomplete realization of the Absolute Truth, people sometimes describe the same Visnu as impersonal Brahman or localized Paramatma.
vadanti tat tattva-vidas
 tattvam yaj jñanam advayam
brahmeti paramatmeti
 bhagavan iti sabdyate
(Bhag. 1.2.11)
From the very beginning, Srimad-Bhagavatam says, satyam param dhimahi: we meditate on the supreme truth. The supreme truth is explained here as jñanam visuddham satyam. The Absolute Truth is devoid of material contamination and is transcendental to the material qualities. It gives all spiritual success and liberation from this material world. That Supreme Absolute Truth is Krsna, Vasudeva. There is no difference between Krsna’s inner self and outward body. Krsna is purna, the complete whole. There is no distinction between His body and soul as there is between ours. Sometimes so-called scholars, not knowing the constitutional position of Krsna, mislead people by saying that the Krsna within is different from the Krsna without. When Krsna says, man-mana bhava mad-bhakto mad-yaji mam namaskuru, so-called scholars advise the reader that it is not the person Krsna to whom we must surrender but the Krsna within. So-called scholars, Mayavadis, cannot understand Krsna with their poor fund of knowledge. One should therefore approach an authorized person to understand Krsna. The spiritual master has actually seen Krsna; therefore he can explain Him properly.
tad viddhi pranipatena
 pariprasnena sevaya
upadeksyanti te jñanam
 jñaninas tattva-darsinah
(Bg. 4.34)
Without approaching an authorized person, one cannot understand Krsna.
Srimad Bhagavatam Canto 05, Chapter 12, Text 10
Srimad Bhagavatam Canto 05, Chapter 12, Text 12