It was at the age of sixteen or seventeen that He traveled to Gayā with a host of His students and there took His spiritual initiation from Īśvara Purī, a Vaiṣṇava sannyāsī and a disciple of the renowned Mādhavendra Purī. Upon His return to Nadia, Nimāi Paṇḍita turned religious preacher, and His religious nature became so strongly represented that Advaita Prabhu, Śrīvāsa and others who had before the birth of Caitanya already accepted the Vaiṣṇava faith were astonished at the change in the young man. He was then no more a contending naiyāyika, a wrangling smārta and a criticizing rhetorician. He swooned at the name of Kṛṣṇa and behaved as an inspired man under the influence of His religious sentiment. It has been described by Murāri Gupta, an eyewitness, that He showed His heavenly powers in the house of Śrīvāsa Paṇḍita in the presence of hundreds of His followers, who were mostly well-read scholars.
It was at this time that He opened a nocturnal school of kīrtana in the compound of Śrīvāsa Paṇḍita with His sincere followers. There He preached, there He sang, there He danced, and there He expressed all sorts of religious feelings. At that time He was joined by Nityānanda Prabhu, who was then a preacher of Vaiṣṇavism and who had completed His travels all over India. In fact, a host of paṇḍita preachers of Vaiṣṇavism, all sincere at heart, came and joined Him from different parts of Bengal. Nadia now became the regular seat of a host of Vaiṣṇava ācāryas whose mission it was to spiritualize mankind with the highest influence of the Vaiṣṇava creed.
The first mandate that He issued to Prabhu Nityānanda and Haridāsa was this: "Go, friends, go through the streets of the town, meet every man at his door and ask him to sing the name of Hari with a holy life, and then come and report to Me every evening the result of your preaching." Thus ordered, the two preachers went out and met Jagāi and Mādhāi, two most abominable characters. These two insulted the preachers on hearing Mahāprabhu's mandate, but were soon converted by the influence of bhakti (devotion) inculcated by their Lord.