CC Madhya 24.172
alabhyā su-cirād api
hariṇā cāśv adeyeti
dvidhā sā syāt su-durlabhā
sādhana — activities of devotional service; oghaiḥ — by masses of; anāsaṅgaiḥ — without attachment; alabhyā — very difficult to achieve; su-cirāt api — even after a considerable duration of time; hariṇā — by the Supreme Lord; ca — also; āśu — very soon; adeyā — not to be delivered; iti — thus; dvidhā — two ways; sā — that; syāt — is; su-durlabhā — very difficult to obtain.
“ ‘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 (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).