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."
Śukadeva Gosvāmī and the wives of the brāhmaṇas who were performing yajña are vivid examples of devotees who achieved the perfectional stage of devotional service by the grace of the Supreme Personality of Godhead.
Persons who have achieved eternal, blissful life exactly on the level of Śrī Kṛṣṇa, and who are able to attract Lord Kṛṣṇa by their transcendental loving service, are called eternally perfect. The technical name is nitya-siddha. There are two classes of living entities—namely, nitya-siddha and nitya-baddha. The distinction is that the nitya-siddhas are eternally Kṛṣṇa conscious without any forgetfulness, whereas the nitya-baddhas, or eternally conditioned souls, are forgetful of their relationship with Kṛṣṇa.