This pure love for God is eternal.
When a person attains to the perfectional stage of love of Godhead, he becomes liberated even in his present body and realizes his constitutional position of immortality. In the Bhagavad-gita (4.9), the Lord says,
Here the Lord says that any person who simply understands His transcendental activities and His appearance and disappearance in this material world becomes liberated, and that after quitting his present body he at once reaches His abode. Therefore it is to be understood that one who has attained the stage of love of God has perfect knowledge, and even if he may fall short of perfect knowledge, he has the preliminary perfection of life that a living entity can attain.
To conceive of oneself as being one with the Supreme is the greatest misconception of self-realization, and this misconception prevents one from rising to the highest stage of love of God. But a person who understands his subordinate position can attain the highest stage of loving service to the Lord. Although the Lord and the living entities are qualitatively one, the living entities are limited, while the Lord is unlimited. This understanding, called amrta-svarupa, makes one eligible for being eternally situated.
In the Srimad-Bhagavatam (10.87.30) the personified Vedas pray to the Lord, “O supreme eternal, if the living entities were equal with You and thus all-pervading and all-powerful like You, there would be no possibility of their being controlled by Your external energy, maya.” Therefore, the living entities should be accepted as fragmental portions of the Supreme. This is confirmed in Bhagavad-gita (15.7) when the Lord says, mamaivamso jiva-loke jiva-bhutah sanatanah: “The living entities are My fragmental portions, eternally.” As fragmental portions, they are qualitatively one with the Supreme, but they are not unlimited.
One who is convinced that he is eternally a servitor of the Supreme Lord is called immortal because he has realized his constitutional position of immortality. Unless one can understand his position as a living entity and an eternal servitor of the Lord, there is no question of immortality. But one who accepts these facts becomes immortal. In other words, those who are under the misconception that the living entity and the Supreme Lord are equal in all respects, both qualitatively and quantitatively, are mistaken, and they are still bound to remain in the material world. They cannot rise to the position of immortality.
Upon attaining love of God, a person immediately becomes immortal and no longer has to change his material body. But even if a devotee of the Lord has not yet reached the perfectional stage of love of Godhead, his devotional service is considered immortal. Any action in the stage of karma or jnana will be finished with the change of body, but devotional service, even if not executed perfectly, will continue into the next life, and the living entity will be allowed to make further progress.
The constitutional position of the living entity as a fragment of the Supreme Lord is confirmed in the Srimad-Bhagavatam and the Upanisads. The Svetasvatara Upanisad (5.9) states,
“If the tip of a hair were divided into one hundred parts, and if one of those parts were again divided into a hundred parts, that one ten-thousandth part of the tip of the hair would be the dimension of the living entity.” As already mentioned, this position of the living entity as a fragment of the Supreme Lord is declared in the Bhagavad-gita (15.7) to be eternal; it cannot be changed. A person who understands his constitutional position as a fragment of the Supreme Lord and engages himself in devotional service with all seriousness at once becomes immortal.
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