When Lord Caitanya described the incarnation for this Age of Kali, Sanātana Gosvāmī, who had been a government minister and was perfectly capable of drawing conclusions, asked the Lord, "How can one understand the advent of an incarnation?" From the description of the incarnation for the Kali millennium, Sanātana Gosvāmī could understand that Lord Caitanya Himself was that incarnation of Kṛṣṇa, and he could also understand that in the future many people would try to imitate Lord Caitanya because the Lord had played as an ordinary brāhmaṇa though His devotees accepted Him as an incarnation. Since Sanātana knew that there would be many pretenders, he asked the Lord, "How can one understand the symptoms of an incarnation?"
"As one can understand the different incarnations for previous millenniums by referring to the Vedic literature," the Lord replied, "one can similarly understand who is actually the incarnation of Godhead in this Age of Kali." In this way the Lord especially stressed reference to authoritative scriptures. In other words, one should not whimsically accept a person as an incarnation but should try to understand the characteristics of an incarnation by referring to the scriptures. An incarnation of the Supreme Lord never declares Himself to be an incarnation, but His followers must ascertain who is an incarnation and who is a pretender by referring to authoritative scriptures.
Any intelligent person can understand the characteristics of a real incarnation by understanding two kinds of features—the principal features, called personal characteristics, and the marginal features, comprising His activities. The scriptures describe both kinds of features. For example, in the beginning of Śrīmad-Bhāgavatam (1.1.1), the features of an incarnation are nicely described. In that verse, the two terms param (supreme) and satyam (truth) are used, and Lord Caitanya indicated that these words reveal Kṛṣṇa's principal feature. The other, marginal features are that He taught Vedic knowledge to Brahmā and incarnated as the puruṣa-avatāra to create the cosmic manifestation. These are occasional features manifested for some special purposes. One should be able to understand and distinguish the principal and marginal features of an avatāra. No one can declare himself an incarnation without referring to these two features. An intelligent man will not accept anyone as an avatāra without studying the principal and marginal features. When Sanātana Gosvāmī tried to confirm Lord Caitanya's personal characteristics as being those of the incarnation for this age, Lord Caitanya Himself indirectly confirmed Sanātana's conclusion by simply saying, "Let us leave aside all these discussions and continue with a description of the śaktyāveśa-avatāras."
The Lord then pointed out that there is no limit to the śaktyāveśa-avatāras but that some can be mentioned as examples. The śaktyāveśa incarnations are of two kinds—direct and indirect. When the Lord Himself comes, He is called a sākṣāt, or direct, śaktyāveśa-avatāra, and when He empowers a living entity to represent Him, that living entity is called an indirect, or āveśa, incarnation. Examples of indirect avatāras are the Four Kumāras, Nārada, Pṛthu and Paraśurāma. These are actually living entities who are given some specific power by the Supreme Personality of Godhead. When a specific opulence of the Supreme Lord is invested in specific entities, they are called āveśa-avatāras. The Four Kumāras represent the Supreme Lord's opulence of knowledge. Nārada represents devotional service to the Supreme Lord. Devotional service is also represented by Lord Caitanya, who is considered the full representation of devotional service. In Brahmā the opulence of creative power is invested, and King Pṛthu is invested with the power for maintaining the living entities. Similarly, in Paraśurāma the power for killing evil elements is invested. As for vibhūti, or the special favor of the Supreme Personality of Godhead, in the Tenth Chapter of the Bhagavad-gītā Lord Kṛṣṇa says that a living entity who is especially powerful or beautiful should be known to be especially favored by the Supreme Lord.
Examples of direct, or sākṣāt, śaktyāveśa-avatāras are the Śeṣa incarnation and the Ananta incarnation. In Ananta the power for sustaining all the planets is invested, and the Śeṣa incarnation is invested with the power for serving the Supreme Lord.
After describing the śaktyāveśa incarnations, Caitanya Mahāprabhu began to speak about the age of the Supreme Lord. He said that the Supreme Lord Kṛṣṇa is always like a sixteen-year-old boy, and when He desires to descend to this universe He first sends His father and mother, who are His devotees, and then He Himself appears. All His activities—beginning with the killing of the Pūtanā demon—are displayed in innumerable universes, and there is no limit to them. Indeed, at every moment, at every second, His manifestations and various pastimes are seen in different universes (brahmāṇḍas). Thus His activities are just like the waves of the Ganges River. Just as there is no limit to the flowing of the waves of the Ganges, there is no cessation of various features of Lord Kṛṣṇa's pastimes in different universes. From childhood He displays many pastimes, and ultimately He exhibits the rāsa dance.
It is said that all the pastimes of Kṛṣṇa are eternal, and this is confirmed in every scripture. Generally people cannot understand how Kṛṣṇa performs His pastimes, but Lord Caitanya clarified this by comparing the performance of His pastimes to the orbit of the sun. According to Vedic astrological calculations, the twenty-four hours of a day are divided into sixty daṇḍas. The days are again divided into 3,600 palas. The sun disc can be perceived crossing the sky in steps of sixty palas each, and that time constitutes a daṇḍa. Eight daṇḍas make one prahara, and the sun rises and sets within four praharas. Similarly, four praharas constitute one night, and after that the sun rises. And just as the sun can be seen in its movement through 3,600 palas, all the pastimes of Kṛṣṇa can be seen in any of the universes.