This is a lecture from the book Caitanya-caritāmṛta, Madhya-līlā 20.97-99 that Srila Prabhupada gave on January 8, 1968 in Los Angeles.
Now, Sanātana Gosvāmī is taking instruction and lessons from Śrī Caitanya Mahāprabhu. And what is the subject matter of instruction? That is described herein by the author of this Caitanya-caritāmṛta. The subject matter is kṛṣṇa-svarūpa, what is the actual position of Kṛṣṇa, kṛṣṇa-svarūpa-mādhuryaiś, and what is the special attractiveness of Kṛṣṇa, mādhurya, kṛṣṇa-svarūpa-mādhurya aiśvarya, and what are the opulences of Kṛṣṇa, bhakti-rasāśrayam. And all these—what is Kṛṣṇa, what is His special qualification for attraction, and what is His opulence—these three things can be understood through devotional service, by no other means. Just like I have several times cited the example that if you want to be in confidence of a great personality, then you must satisfy him by your service. You cannot understand a big man by your speculation. Even in this material world, if you want to know a big man, what he is, then you must satisfy him by your service attitude, by friendship, by love, and he will disclose to you what he is. So the same process is bhakti-rasāśrayam. If you want to know what is Kṛṣṇa, what is His opulence, what is special feature for attraction, then you should try to understand through this devotional service of Kṛṣṇa consciousness.
In the Bhagavad-gītā also, the Lord says that bhaktyā mām abhijānāti. Bhaktyā mām abhijānāti, tattvataḥ, yāvān yaś cāsmi tattvataḥ [Bg. 18.55]. In another place the Lord says that "To understand Me, actually what I am, is very difficult." Manuṣyāṇāṁ sahasreṣu kaścid yatati siddhaye: [Bg. 7.3] "Out of many millions of human beings, somebody tries to make a perfection of his life." Otherwise they are all working like cats and dogs, that's all, simply āhāra-nidrā-bhaya-maithunaṁ ca. They have no other information. "Work hard, eat, be merry and enjoy, and have mating, that's all." So out of millions and millions of persons like this, engaged in animal propensities of life, only a few persons, selected person... Because the illusory energy has grasped us under her clutches very tightly, to get out of the clutches is very difficult. So somehow or other, a few people, out of many millions and thousands, they come to the understanding that what is the real perfection of life. Now, those who are actually perfected, out of them, out of millions of them, one can understand Kṛṣṇa. That is the statement of Bhagavad-gītā. Manuṣyāṇāṁ sahasreṣu kaścid yatati siddhaye, yatatām api siddhānām [Bg. 7.3]. Siddhānām means those who are already achieved perfection. Out of them—not these imperfect fools—those who are actually attained perfection, they can understand what Kṛṣṇa is actually, tattvataḥ. And that actual position can be understood... In another place in Bhagavad-gītā it says, bhaktyā mām abhijānāti: [Bg. 18.55] "What He is actually, that can be understood by this devotional service, no other process." No other process will help to understand Kṛṣṇa. You can... By other processes you can achieve some other thing, but if you want to know Kṛṣṇa, then you have to understand through your devotional service. Bhaktyā mām abhijānāti yāvān yaś cāsmi tattvataḥ: [Bg. 18.55] "As I am." Tato māṁ tattvato jnātvā.
So you will have entrance into the spiritual kingdom, into the abode of Kṛṣṇa when you have perfectly... We cannot understand perfectly, but as far as possible, as far we have got the capacity, if we understand Kṛṣṇa as He is, then the entrance will be there. Otherwise there is no entrance. Therefore Lord Caitanya instructed Sanātana Gosvāmī about Kṛṣṇa through devotional service. This instruction is very important. You should very carefully hear and, if possible, note. This is directly the instruction. Just like the Bhagavad-gītā: the Lord Kṛṣṇa is directly instructing Arjuna. But in the Bhagavad-gītā there are many phases of instruction, fruitive action, philosophical speculation, yoga system and jnāna system, all kinds of different paths. Ultimately, of course, Lord Kṛṣṇa instructed him that sarva-dharmān parityajya mām ekaṁ śaraṇaṁ vraja [Bg. 18.66]. That is the most confidential part. But here Lord Caitanya, He is not instructing any superfluous things. So that is the blessings of Lord Caitanya. Even what Kṛṣṇa could not give, what Kṛṣṇa could not, or Kṛṣṇa hesitated to give... Because Kṛṣṇa hesitated that "If I speak in the beginning of the Bhagavad-gītā, sarva-dharmān parityajya mām ekaṁ śaraṇaṁ vraja [Bg. 18.66], people would not accept it." There was no necessity of describing Bhagavad-gītā in so many phases of instruction. Because the last instruction, most confidential instruction, was that "You give up everything and just surrender unto Me." That is the actual instruction of Bhagavad-gītā, but that was not spoken in the beginning because there are many phases of human beings. They are under different stages of...