CC Ādi 16.15
nāma-saṅkīrtana kara, — upadeśa kaila
The Lord, being satisfied, instructed him about the object of life and the process for attaining it. He instructed him that the basic principle of success is to chant the holy name of the Lord [the Hare Kṛṣṇa mahā-mantra].
The Kṛṣṇa consciousness movement is based upon this instruction of Lord Caitanya Mahāprabhu that one must chant the Hare Kṛṣṇa mahā-mantra regularly and according to the prescribed principles. We simply ask our Western students to chant at least sixteen rounds a day, but sometimes we find that they fail to chant even these sixteen rounds, and instead they bring many austere books and a worshiping method that diverts their attention in so many ways. Śrī Caitanya Mahāprabhu’s cult is based upon the chanting of the Hare Kṛṣṇa mantra. Lord Caitanya first advised Tapana Miśra to fix his mind on this chanting. We, the members of the Kṛṣṇa consciousness movement, must strictly follow this advice of Caitanya Mahāprabhu.