1. Krsna personally inaugurates the religion of the age-nama-sankirtana-as Lord Caitanya:

(Lord Krsna, thinking to Himself ) "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. "
Cc. Adi 3.19

2. The Kali-yuga dharma, chanting the holy name, is introduced by Lord Caitanya:

(Karabhajana Rsi to Maharaj Nimi): "Accompanied by His personal devotees, Lord Kṛṣṇa, assuming a golden color, introduces the hari-nāma-saṅkīrtana, the chanting of the Hare Kṛṣṇa mantra, in the Age of Kali. By this process, He delivers love for Kṛṣṇa to the general populace. Lord Kṛṣṇa, the son of Nanda Mahārāja, personally introduces the occupational duty of the Age of Kali. He personally chants and dances in ecstatic love, and thus the entire world chants congregationally."
Cc. Madhya 20.340-41

3. Krsna came again as Lord Caitanya to teach us the path by which to cross the ocean of Kali-yuga:

Just before the beginning of Kali-yuga—or, in other words, at the end of Dvāpara-yuga—Lord Śrī Kṛṣṇa appeared and left His instructions in the form of Bhagavad-gītā, in which He asked all living entities to surrender unto Him. Since the beginning of Kali-yuga, however, people have practically been unable to surrender to the lotus feet of Kṛṣṇa, and therefore, after some five thousand years, Kṛṣṇa came again as Śrī Caitanya Mahāprabhu just to teach the entire world how to surrender unto Him, unto Śrī Kṛṣṇa, and thus be purified...

Kali-yuga is full of contamination. This is described in the Śrīmad-Bhāgavatam (12.3.51):

This age of Kali is full of unlimited faults. Indeed, it is just like an ocean of faults (doṣa-nidhi). But there is one chance, one opportunity. Kīrtanād eva kṛṣṇasya mukta-saṅgaḥ paraṁ vrajet: simply by chanting the Hare Kṛṣṇa mantra, one can be freed from the contamination of Kali-yuga and, in his original spiritual body, can return home, back to Godhead. This is the opportunity of Kali-yuga.

When Kṛṣṇa appeared, He gave His orders, and when Kṛṣṇa Himself appeared as a devotee, as Śrī Caitanya Mahāprabhu, He showed us the path by which to cross the ocean of Kali-yuga. That is the path of the Hare Kṛṣṇa movement. When Śrī Caitanya Mahāprabhu appeared, He ushered in the era for the saṅkīrtana movement. It is also said that for ten thousand years this era will continue. This means that simply by accepting the saṅkīrtana movement and chanting the Hare Kṛṣṇa mahā-mantra, the fallen souls of this Kali-yuga will be delivered. After the Battle of Kurukṣetra, at which Bhagavad-gītā was spoken, Kali-yuga continues for 432,000 years, of which only 5,000 years have passed. Thus there is still a balance of 427,000 years to come. Of these 427,000 years, the 10,000 years of the saṅkīrtana movement inaugurated by Śrī Caitanya Mahāprabhu 500 years ago provide the opportunity for the fallen souls of Kali-yuga to take to the Kṛṣṇa consciousness movement, chant the Hare Kṛṣṇa mahā-mantra and thus be delivered from the clutches of material existence and return home, back to Godhead.

Chanting of the Hare Kṛṣṇa mahā-mantra is potent always, but it is especially potent in this age of Kali. Therefore Śukadeva Gosvāmī, while instructing Mahārāja Parīkṣit, stressed this chanting of the Hare Kṛṣṇa mantra.

“My dear King, although Kali-yuga is full of faults, there is still one good quality about this age. It is that simply by chanting the Hare Kṛṣṇa mahā-mantra, one can become free from material bondage and be promoted to the transcendental kingdom.” (Bhāg. 12.3.51) Those who have accepted the task of spreading the Hare Kṛṣṇa mahā-mantra in full Kṛṣṇa consciousness should take this opportunity to deliver people very easily from the clutches of material existence. Our duty, therefore, is to follow the instructions of Śrī Caitanya Mahāprabhu and preach the Kṛṣṇa consciousness movement all over the world very sincerely. This is the best welfare activity for the peace and prosperity of human society.
Bhag. 8.5.23