CC Madhya 6.241
prabhu upadeśa kaila nāma-saṅkīrtana
Then the Bhaṭṭācārya asked Caitanya Mahāprabhu, “Which item is most important in the execution of devotional service?” The Lord replied that the most important item was the chanting of the holy name of the Lord.
There are nine items to be executed in devotional service. These are enumerated in the following verse from Śrīmad-Bhāgavatam (7.5.23):
arcanaṁ vandanaṁ dāsyaṁ sakhyam ātma-nivedanam
Hearing the glories of the Lord, chanting, remembering, serving the lotus feet of the Lord, offering worship in the temple, offering prayers, becoming a servant of the Lord, becoming the Lord’s friend, and sarvātma-nivedana, offering oneself fully at the lotus feet of the Lord — these are the nine devotional processes. In The Nectar of Devotion, these are expanded into sixty-four items. When Sārvabhauma Bhaṭṭācārya asked the Lord which item was most important, Śrī Caitanya Mahāprabhu immediately answered that the most important item is the chanting of the holy names of the Lord — Hare Kṛṣṇa, Hare Kṛṣṇa, Kṛṣṇa Kṛṣṇa, Hare Hare/ Hare Rāma, Hare Rāma, Rāma Rāma, Hare Hare. He then quoted the following verse from the Bṛhan-nāradīya Purāṇa (thirty-eighth chapter, verse 126) to confirm His statement.