CC Ādi 7.18-19
yāṅ-sabā lañā prabhura kīrtana-pracāra
yāṅ-sabā lañā dāna kare prema-dhana
Distinguishing between pure devotees and internal or confidential devotees, Śrī Rūpa Gosvāmī, in his book Upadeśāmṛta, traces the following gradual process of development. Out of many thousands of karmīs, one is better when he is situated in perfect Vedic knowledge. Out of many such learned scholars and philosophers, one who is actually liberated from material bondage is better, and out of many such persons who are actually liberated, one who is a devotee of the Supreme Personality of Godhead is considered to be the best. Among the many such transcendental lovers of the Supreme Personality of Godhead, the gopīs are the best, and among the gopīs Śrīmatī Rādhikā is the best. Śrīmatī Rādhikā is very dear to Lord Kṛṣṇa, and similarly Her ponds, namely, Śyāma-kuṇḍa and Rādhā-kuṇḍa, are also very dear to the Supreme Personality of Godhead.
Śrīla Bhaktisiddhānta Sarasvatī Ṭhākura comments in his Anubhāṣya that among the five tattvas, two are energies (śakti-tattva) and the three others are energetic (śaktimān tattva). Unalloyed and internal devotees are both engaged in the favorable culture of Kṛṣṇa consciousness untinged by philosophical speculation or fruitive activities. They are all understood to be pure devotees, and those among them who simply engage in conjugal love are called mādhurya-bhaktas, or internal devotees. The loving services in parental love, fraternity and servitude are included in conjugal love of God. In conclusion, therefore, every confidential devotee is a pure devotee of the Lord.
Śrī Caitanya Mahāprabhu enjoys His pastimes with His immediate expansion Nityānanda Prabhu. His pure devotees and His three puruṣa incarnations, namely, Kāraṇodakaśāyī Viṣṇu, Garbhodakaśāyī Viṣṇu and Kṣīrodakaśāyī Viṣṇu, always accompany the Supreme Lord to propound the saṅkīrtana movement.