Pradyumna: "In the same Bhagavad-gītā (BG 18.55) it is also said that scientific knowledge of Śrī Kṛṣṇa is understood only by the process of devotional service, or bhakti-yoga . . ."
Prabhupāda: Yes. Here also it is confirmed: bhagavad-bhakti-yogataḥ. It is not said: "By mystic yoga, by haṭha-yoga, by jñāna-yoga, by karma-yoga." No. Bhagavad-bhakti-yogataḥ. If you want to understand the science of God, then we have to adopt this devotional service. Not by other yogas. Otherwise, in Bhāgavata it would have been said, "By karma-yogataḥ, by jñāna-yogataḥ, by haṭha-yogataḥ, by dhyāna-yogataḥ."
No. It is clearly said, bhagavad-bhakti-yogataḥ. Bhagavat-tattva-vijñānaṁ mukta-saṅgasya jāyate (SB 1.2.20). If you are still after jñāna-yoga, dhyāna-yoga, you cannot understand Kṛṣṇa, God. It is clearly said. In the Bhagavad-gītā also, it is clearly said, bhaktyā mām abhijānāti (BG 18.55): simply through devotional service.
So if you want to know God, then you have to follow the prescribed rules and regulation of bhagavad-bhakti-yoga. It is very simple. It is made very easy, especially in this age: simply by chanting Hare Kṛṣṇa mantra. It's so made easy, but we are so unfortunate that we do not take advantage of this. Etādṛśī tava kṛpā bhagavan mamāpi durdaivam īdṛśam ihājani nānurāgaḥ (CC Antya 20.16, Śikṣāṣṭaka 2).
Lord Caitanya Mahāprabhu laments, "My dear Lord, You are so compassionate and merciful upon us that in this age You have descended in Your . . . as Your name, and one can chant this name without any regulation." Without any regulation. Niyamitaḥ smaraṇe na kālaḥ (CC Antya 20.16). Any time, any circumstances, one can chant this Hare Kṛṣṇa mantra. Kṛṣṇa has become so liberal.
But Caitanya Mahāprabhu says, etādṛśī tava kṛpā bhagavan mamāpi: "My dear Lord, although You are so much merciful upon me, still, I am so unfortunate." Etādṛśī tava kṛpā bhagavan mamāpi durdaivam īdṛśam, "I am so unfortunate," durdaivam īdṛśam ihājani na, "I could not be attached to chanting of Hare Kṛṣṇa mantra. Oh, I am so unfortunate." You see? The things have been made so easy, actually, but unfortunate class of men, they cannot take to it.