In the Satya-yuga the process of self-realization was meditation, and this process is taught by the white incarnation of God. This incarnation gave a benediction to the sage Kardama by which he could have an incarnation of the Personality of Godhead as his son. In the Satya-yuga, everyone meditated on Kṛṣṇa, and each and every living entity was in full knowledge. In this present age, Kali-yuga, people who are not in full knowledge are still attempting this meditative process which was recommended for a previous age. The process for self-realization recommended in the Tretā millennium was the performance of sacrifice, and this was taught by the red incarnation of God. In the Dvāpara millennium, Kṛṣṇa was personally present, and He was worshiped by everyone by the mantra:
- namas te vāsudevāya
- namaḥ saṅkarṣaṇāya
- pradyumnāyāniruddhāya
- tubhyaṁ bhagavate namaḥ
"Let me offer my obeisances unto the Supreme Personality of Godhead, Vāsudeva, Saṅkarṣaṇa, Pradyumna, and Aniruddha." This was the process of self-realization for the Dvāpara age. In the next millennium—this present age of Kali-yuga—the Lord incarnates to preach the chanting of the holy name of Kṛṣṇa. In this age the Lord is yellow (Caitanya Mahāprabhu), and He teaches people love of God by chanting the names of Kṛṣṇa. This teaching is carried out personally by Kṛṣṇa, and He exhibits love of Godhead by chanting, singing and dancing with thousands of people following Him. This particular incarnation of the Supreme Personality of Godhead is foretold in Śrīmad-Bhāgavatam (11.5.32):
- kṛṣṇa-varṇaṁ tviṣākṛṣṇaṁ
- sāṅgopāṅgāstra-pārṣadam
- yajñaiḥ saṅkīrtana-prāyair
- yajanti hi sumedhasaḥ
"In the age of Kali the Lord incarnates as a devotee, yellowish in color, and is always chanting Hare Kṛṣṇa, Hare Kṛṣṇa, Kṛṣṇa Kṛṣṇa, Hare Hare/ Hare Rāma, Hare Rāma, Rāma Rāma, Hare Hare. Although He is Kṛṣṇa, His complexion is not blackish like Kṛṣṇa's in Dvāpara-yuga but is golden. It is in Kali-yuga that the Lord engages in preaching love of Godhead through the saṅkīrtana movement, and those living entities who are intelligent adopt this process of self-realization." It is also stated in Śrīmad-Bhāgavatam (12.3.52):
- kṛte yad dhyāyato viṣṇuṁ
- tretāyāṁ yajato makhaiḥ
- dvāpare paricaryāyāṁ
- kalau taddhari-kīrtanāt
"The self-realization which was achieved in the Satya millennium by meditation, in the Tretā millennium by the performance of different sacrifices, and in the Dvāpara millennium by worship of Lord Kṛṣṇa, can be achieved in the age of Kali simply by chanting the holy names, Hare Kṛṣṇa." This is also confirmed in Viṣṇu Purāṇa (6.2.17) where it is stated:.
- dhyāyan kṛte yajan yajñais
- tretāyāṁ dvāpare 'rcayan
- yad āpnoti tad āpnoti
- kalau saṅkīrtya keśavam
"In this age there is no use in meditation, sacrifice and temple worship. Simply by chanting the holy name of Kṛṣṇa—Hare Kṛṣṇa, Hare Kṛṣṇa, Kṛṣṇa Kṛṣṇa, Hare Hare/ Hare Rāma, Hare Rāma, Rāma Rāma, Hare Hare—one can achieve perfect self-realization."
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, directly asked of the Lord, "How can one understand the advent of an incarnation?" By the description of the incarnation for the Kali millennium, Sanātana Gosvāmī could understand that Lord Caitanya was indeed that incarnation of Kṛṣṇa, and he could also understand that in the future there would be many people who would try to imitate Lord Caitanya because the Lord played as an ordinary brāhmaṇa, despite the fact that 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?"