When a person is never tired of executing devotional service and is always engaged in Kṛṣṇa conscious activities, constantly relishing the transcendental mellows in relationship with Kṛṣṇa, the devotee is called perfect. This perfectional stage can be achieved in two ways: one may achieve this stage of perfection by gradual progress in devotional service, or one may become perfect by the causeless mercy of Kṛṣṇa, even though he has not executed all the details of devotional service. There is the following nice statement in the Third Canto, 15th Chapter, 25th verse, of Śrīmad-Bhāgavatam describing a devotee who achieves perfection by regularly executing devotional service: A person who is freed from the false egotism of material existence, or an advanced mystic, is eligible to enter into the kingdom of God known as Vaikuṇṭha. Such a mystic becomes so joyful by constant execution of the regulative principles of devotional service that he thereby achieves the special favor of the Supreme Lord. Yamarāja, the mighty superintendent of death, is afraid to go near such a devotee; so we can imagine the potency of advanced devotional service, especially when devotees sit together and engage in talking of the pastimes of the Supreme Personality of Godhead. Those devotees express their feelings in such a way that they automatically melt with ecstasy, and many transcendental symptoms become manifested in their bodies. Anyone desiring advancement in devotional service must follow in the footsteps of such devotees.
Prahlād Mahārāj 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 the 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 began to say, "How wonderful it is that although these women have undertaken no reformatory performances such as accepting the sacred thread, have not resided in the monastaries of the spiritual master, have not observed the strict principles of celibacy, have not undergone any austerities, nor philosophized upon the observance of all 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."