Prahlāda Mahārāja said that no one can attain the perfectional stage of devotional service without bowing down before exalted devotees. Learned sages like Mārkaṇḍeya Ṛṣi attained perfection in devotional service simply by executing such regulative principles of service.
A person's achieving perfection in devotional service simply by the causeless mercy of the Lord is explained in Śrīmad-Bhāgavatam in connection with the brāhmaṇas and their wives who were engaged in performing yajña, or sacrifice. When the wives of the brāhmaṇas were favored by Lord Kṛṣṇa and immediately attained the ecstasy of love of Godhead, their husbands said, "How wonderful it is that although these women have undertaken no reformatory performances such as accepting the sacred thread, have not resided in the monasteries of the spiritual master, have not observed the strict principles of celibacy, have not undergone any austerities and have not philosophized upon the observance of ritualistic ceremonies, they still have attained the favor of Kṛṣṇa, which is aspired after even by great mystics! How wonderful it is that these women have attained such perfection, while we, although brāhmaṇas who have performed all the reformatory activities, cannot attain to this advanced stage!"
There is a similar statement by Nārada, addressed to Śukadeva Gosvāmī: "My dear Śukadeva Gosvāmī, you never took the trouble to reside under the care of a spiritual master, and yet you have attained such a great status of transcendental knowledge. You never took the trouble to undergo severe austerities, and still, how wonderful it is that you have been situated in the most perfect stage of love of Godhead."
Śukadeva Gosvāmī and the wives of the brāhmaṇas performing yajña are vivid examples of devotees who achieved the perfectional stage of devotional service by the grace of the Supreme Personality of Godhead.