CC Madhya 19.169

ei ‘śuddha-bhakti’ — ihā haite ‘premā’ haya
pañcarātre, bhāgavate ei lakṣaṇa kaya
Word for word: 
ei — this; śuddha-bhakti — pure devotional service; ihā haite — from which; premā — unalloyed love of Kṛṣṇa; haya — there is; pañcarātre — in the Vedic literatures known as the Pañcarātras; bhāgavate — also in the Śrīmad-Bhāgavatam; ei — these; lakṣaṇa — symptoms; kaya — are described.
Translation: 
“These activities are called śuddha-bhakti, pure devotional service. If one renders such pure devotional service, he develops his original love for Kṛṣṇa in due course of time. In Vedic literatures like the Pañcarātras and Śrīmad-Bhāgavatam, these symptoms are described.
Purport: 

One has to develop his devotional service under the directions of a pure devotee, the spiritual master, and in accordance with the Vedic directions given in the Pañcarātra and Bhāgavata systems. The Pañcarātra system includes methods of temple worship, and the Bhāgavata system includes the spreading of Kṛṣṇa conscious philosophy through the recitation of Śrīmad-Bhāgavatam and the discussion of philosophy with people who are interested. Through discussion, one can create an interest and understanding of the Pañcarātra and Bhāgavata systems.