Unless one is attached to Krsna, he cannot attain devotional perfection even if he renders devotional service for a long time. Krsna does not easily deliver perfection in devotional service

Expressions researched:
"Devotional perfection is very difficult to attain for two reasons. First, unless one is attached to Kṛṣṇa, he cannot attain devotional perfection even if he renders devotional service for a long time. Second, Kṛṣṇa does not easily deliver perfection in devotional service"

Sri Caitanya-caritamrta

CC Madhya-lila

Devotional perfection is very difficult to attain for two reasons. First, unless one is attached to Kṛṣṇa, he cannot attain devotional perfection even if he renders devotional service for a long time. Second, Kṛṣṇa does not easily deliver perfection in devotional service.

CC Madhya 24.172, Translation and Purport

Devotional perfection is very difficult to attain for two reasons. First, unless one is attached to Kṛṣṇa, he cannot attain devotional perfection even if he renders devotional service for a long time. Second, Kṛṣṇa does not easily deliver perfection in devotional service.

As stated in Śrīmad-Bhāgavatam (SB 5.6.18), muktiṁ dadāti karhicit. Śrīla Śukadeva Gosvāmī told Mahārāja Parīkṣit that Kṛṣṇa readily grants liberation but does not very readily grant perfection in devotional service. This means that Kṛṣṇa wants to see that a devotee is actually sincere and serious and that he does not have ulterior motives. If this is the case, devotional service can very easily be successful; otherwise it is very difficult to obtain from the Supreme Personality of Godhead. This verse appears in the Bhakti-rasāmṛta-sindhu (1.1.35).