There are various kinds of avatāras, such as puruṣāvatāras, guṇāvatāras, līlāvatāras, śakty-āveśa avatāras, manvantara-avatāras and yugāvatāras—all appearing on schedule all over the universe. But Lord Kṛṣṇa is the primeval Lord, the fountainhead of all avatāras. Lord Śrī Kṛṣṇa descends for the specific purpose of mitigating the anxieties of the pure devotees, who are very anxious to see Him in His original Vṛndāvana pastimes. Therefore, the prime purpose of the Kṛṣṇa avatāra is to satisfy His unalloyed devotees. The Lord says that He incarnates Himself in every millennium. This indicates that He incarnates also in the Age of Kali. As stated in the Śrīmad-Bhāgavatam, the incarnation in the Age of Kali is Lord Caitanya Mahāprabhu, who spread the worship of Kṛṣṇa by the saṅkīrtana movement (congregational chanting of the holy names) and spread Kṛṣṇa consciousness throughout India. He predicted that this culture of saṅkīrtana would be broadcast all over the world, from town to town and village to village. Lord Caitanya as the incarnation of Kṛṣṇa, the Personality of Godhead, is described secretly but not directly in the confidential parts of the revealed scriptures, such as the Upaniṣads, Mahābhārata and Bhāgavatam. The devotees of Lord Kṛṣṇa are very much attracted by the saṅkīrtana movement of Lord Caitanya. This avatāra of the Lord does not kill the miscreants, but delivers them by His causeless mercy.
(Bhagavad Gita-------4:8------purport).