Attaining scientific knowledge of the Personality of Godhead means seeing one's own self simultaneously. As far as the identity of the living being as spirit self is concerned, there are a number of speculations and misgivings. The materialist does not believe in the existence of the spirit self, and empiric philosophers believe in the impersonal feature of the whole spirit without individuality of the living beings. But the transcendentalists affirm that the soul and the Supersoul are two different identities, qualitatively one but quantitatively different. There are many other theories, but all these different speculations are at once cleared off as soon as Śrī Kṛṣṇa is realized in truth by the process of bhakti-yoga. Śrī Kṛṣṇa is like the sun, and the materialistic speculations about the Absolute Truth are like the darkest midnight. As soon as the Kṛṣṇa sun is arisen within one's heart, the darkness of materialistic speculations about the Absolute Truth and the living beings is at once cleared off. In the presence of the sun, the darkness cannot stand, and the relative truths that were hidden within the dense darkness of ignorance become clearly manifested by the mercy of Kṛṣṇa, who is residing in everyone's heart as the Supersoul.
In the Bhagavad-gītā (BG 10.11) the Lord says that in order to show special favor to His pure devotees, He personally eradicates the dense darkness of all misgivings by switching on the light of pure knowledge within the heart of a devotee. Therefore, because of the Personality of Godhead's taking charge of illuminating the heart of His devotee, certainly a devotee, engaged in His service in transcendental love, cannot remain in darkness. He comes to know everything of the absolute and the relative truths. The devotee cannot remain in darkness, and because a devotee is enlightened by the Personality of Godhead, his knowledge is certainly perfect. This is not the case for those who speculate on the Absolute Truth by dint of their own limited power of approach. Perfect knowledge is called paramparā, or deductive knowledge coming down from the authority to the submissive aural receiver who is bona fide by service and surrender. One cannot challenge the authority of the Supreme and know Him also at the same time. He reserves the right of not being exposed to such a challenging spirit of an insignificant spark of the whole, a spark subjected to the control of illusory energy. The devotees are submissive, and therefore the transcendental knowledge descends from the Personality of Godhead to Brahmā and from Brahmā to his sons and disciples in succession. This process is helped by the Supersoul within such devotees. That is the perfect way of learning transcendental knowledge.
This enlightenment perfectly enables the devotee to distinguish spirit from matter because the knot of spirit and matter is untied by the Lord. This knot is called ahaṅkāra, and it falsely obliges a living being to become identified with matter. As soon as this knot is loosened, therefore, all the clouds of doubt are at once cleared off. One sees his master and fully engages himself in the transcendental loving service of the Lord, making a full termination of the chain of fruitive action. In material existence, a living being creates his own chain of fruitive work and enjoys the good and bad effects of those actions life after life. But as soon as he engages himself in the loving service of the Lord, he at once becomes free from the chain of karma. His actions no longer create any reaction.