One may ask that if Caitanya Mahāprabhu is Kṛṣṇa Himself, then why did He need a spiritual master? Of course He did not need a spiritual master, but because He was playing the role of ācārya (one who teaches by example), He accepted a spiritual master. Even Kṛṣṇa Himself accepted a spiritual master, for that is the system. In this way the Lord sets the example for men. We should not think, however, that the Lord takes a spiritual master because He is in want of knowledge. He is simply stressing the importance of accepting the disciplic succession. The knowledge of that disciplic succession actually comes from the Lord Himself, and if the knowledge descends unbroken, it is perfect. Although we may not be in touch with the original personality who first imparted the knowledge, we may receive the same knowledge through this process of transmission. In Śrīmad-Bhāgavatam it is stated that Kṛṣṇa, the Absolute Truth, the Personality of Godhead, transmitted transcendental knowledge into the heart of Brahmā. This, then, is one way knowledge is received—through the heart. Thus there are two processes by which one may receive knowledge: One depends directly upon the Supreme Personality of Godhead, who is situated as the Supersoul within the heart of all living entities, and the other depends upon the guru, or spiritual master, who is an expansion of Kṛṣṇa. Thus Kṛṣṇa transmits information both from within and from without. We simply have to receive it. If knowledge is received in this way, it doesn’t matter whether it is inconceivable or not.
In Śrīmad-Bhāgavatam there is a great deal of information given about the Vaikuṇṭha planetary systems, which are beyond the material universe. Similarly, a great deal of inconceivable information is given in the Caitanya-caritāmṛta. Any attempt to arrive at this information through experimental knowledge will fail. The knowledge simply has to be accepted. According to the Vedic method, śabda, or transcendental sound, is regarded as evidence. Sound is very important in Vedic understanding, for, if it is pure, it is accepted as authoritative. Even in the material world we accept a great deal of information sent thousands of miles by telephone or radio. In this way we also accept sound as evidence in our daily lives. Although we cannot see the informant, we accept his information as valid on the basis of sound. Sound vibration, then, is very important in the transmission of Vedic knowledge.
The Vedas inform us that beyond this cosmic manifestation there are extensive planets in the spiritual sky. This material manifestation is regarded as only a small portion of the total creation. The material manifestation includes not only this universe but innumerable others as well, but all the material universes combined constitute only one fourth of the total creation. The remaining three fourths is situated in the spiritual sky. In that sky innumerable planets float, and these are called Vaikuṇṭhalokas. In every Vaikuṇṭhaloka, Nārāyaṇa presides with His four expansions: Saṅkarṣaṇa, Pradyumna, Aniruddha and Vāsudeva. This Saṅkarṣaṇa, states Kṛṣṇadāsa Kavirāja in the eighth verse of the Caitanya-caritāmṛta, is Lord Nityānanda.