The desire of the Lord to appear in Kali-yuga as Śrī Caitanya Mahāprabhu was born from a twofold purpose: internally, to experience the super-excellent love (mahābhāva) of Śrīmatī Rādhārāṇī, ; and externally, to inaugurate the saṅkīrtana movement—the congregational chanting of the holy names[i]— Hare Kṛṣṇa, Hare Kṛṣṇa, Kṛṣṇa Kṛṣṇa, Hare Hare / Hare Rāma, Hare Rāma, Rāma Rāma, Hare Hare.
The Internal Reasons: The Mahābhāva of Śrīmatī Rādhārāṇī
The Internal Reason is of two purposes, one is to taste the love of Radharani and the other is
There is a supreme symptom of ecstatic love which is called mahābhāva. This mahābhāva expression was possible only in Rādhārāṇī, but later on when Śrī Kṛṣṇa Caitanya appeared in order to feel the mode of love of Rādhārāṇī, He also expressed all of the symptoms of mahābhāva. Śrī Rūpa Gosvāmī says in this connection that when the symptoms of ecstatic love become the most bright, that stage is accepted as mahābhāva.
Viṣaya and Āśraya
“Viṣaya and āśraya are two very significant words relating to the reciprocation between Kṛṣṇa and His devotee. The devotee is called the āśraya, and his beloved, Kṛṣṇa, is the viṣaya. Different ingredients are involved in the exchange of love between the āśraya and viṣaya, which are known as vibhāva, anubhāva, sāttvika and vyabhicārī. Vibhāva is divided into the two categories ālambana and uddīpana. Ālambana may be further divided into āśraya and viṣaya. In the loving affairs of Rādhā and Kṛṣṇa, Rādhārāṇī is the āśraya feature and Kṛṣṇa the viṣaya. The transcendental consciousness of the Lord tells Him, “I am Kṛṣṇa, and I experience pleasure as the viṣaya. The pleasure enjoyed by Rādhārāṇī, the āśraya, is many times greater than the pleasure I feel.” Therefore, to feel the pleasure of the āśraya category, Lord Kṛṣṇa appeared as Śrī Caitanya Mahāprabhu.”
[ 04. Śrī Caitanya-caritāmṛta / Ādi-līlā / Ādi 4: The Confidential Reasons for the Appearance of Śrī Caitanya Mahāprabhu / Ādi 4.135]
The External Reason: The Saṅkīrtana Movement
According to the specific yuga-dharma (the religious practice for the age), the Lord is worshipped accordingly. A detailed description of the various modes of worship in each yuga, as well as the Lord's transcendental names, forms, and paraphernalia for each yoga (age) can be found in the Śrīmad-Bhāgavatam 11.5.19-32 in a conversation between King Nimi and Śrī Karabhājana.
Regarding the mode of worship in each yuga; in Satya-yuga, the Lord was worshipped through austere meditation and sense control; in Tretā-yuga, through the rituals enjoined in the three Vedas—Sāma, Yajur and Ṛg.; and in Dvāpara-yuga, through worshipping the Lord in pomp and ceremony, as one would honor the royal order; but, in the current age of Kali-yuga, simply by chanting the mahā-mantra, Hare Kṛṣṇa, Hare Kṛṣṇa Kṛṣṇa Kṛṣṇa, Hare Hare / Hare Rāma, Hare Rāma, Rāma Rāma, Hare Hare, anyone can achieve the highest goal of life—Kṛṣṇa-prema.
yuga-dharma pravartāimu nāma-saṅkīrtana
cāri bhāva-bhakti diyā nācāmu bhuvana
“I shall personally inaugurate the religion of the age—nāma-saṅkīrtana, the congregational chanting of the holy name. I shall make the world dance in ecstasy, realizing the four mellows of loving devotional service.” [Śrī Caitanya-caritāmṛta, Ādi-līlā 3.19]
yajanti hi su-medhasaḥ
“In the Age of Kali, intelligent persons perform congregational chanting to worship the incarnation of Godhead who constantly sings the name of Kṛṣṇa. Although His complexion is not blackish, He is Kṛṣṇa Himself. He is accompanied by His associates, servants, weapons and confidential companions.” [Śrī Caitanya-caritāmṛta, Ādi 3.52]
kṛṣṇa-varṇam—repeating the syllables kṛṣ-ṇa; tviṣā—with a luster; akṛṣṇam—not black (golden); sa-aṅga—along with associates; upāṅga—servitors; astra—weapons;
āpani karimu bhakta-bhāva aṅgīkāre
āpani ācari’ bhakti śikhāimu sabāre
“I shall accept the role of a devotee, and I shall teach devotional service by practicing it Myself.” [Śrī Caitanya-caritāmṛta, Ādi-līlā 3.20:]
sanātana kahe,—“yāte īśvara-lakṣaṇa
Sanātana Gosvāmī said, “The color of the personality in whom the characteristics of the Lord are found is yellowish. His activities include the distribution of love of Godhead and the chanting of the holy names of the Lord.
[ 04. Śrī Caitanya-caritāmṛta / Madhya-līlā / Madhya 20: Lord Śrī Caitanya Mahāprabhu Instructs Sanātana Gosvāmī in the Science of the Absolute Truth / Madhya 20.364]