The results of our activities must be used to serve the interest of the Lord, and not for any other purpose. Only by serving the Lord's interest can we perceive the ātma-bhūta interest mentioned herein. The ātma-bhūta interest mentioned in this mantra and the brahma-bhūta (SB 4.30.20) interest mentioned in the Bhagavad-gītā (18.54) are one and the same. The supreme ātmā, or soul, is the Lord Himself, and the minute ātmā is the living entity. The supreme ātmā, or Paramātmā, alone maintains all the individual minute beings, for the Supreme Lord wants to derive pleasure out of their affection. The father extends himself through his children and maintains them in order to derive pleasure. If the children obey the father's will, family affairs will run smoothly, with one interest and a pleasing atmosphere. The same situation is transcendentally arranged in the absolute family of the Parabrahman, the Supreme Spirit.
The Parabrahman is as much a person as the individual entities. Neither the Lord nor the living entities are impersonal. Such transcendental personalities are full of transcendental bliss, knowledge and life eternal. That is the real position of spiritual existence, and as soon as one is fully cognizant of this transcendental position, he at once surrenders unto the lotus feet of the Supreme Being, Śrī Kṛṣṇa. But such a mahātmā, or great soul, is very rarely seen because such transcendental realization is achieved only after many, many births. Once it is attained, however, there is no longer any illusion or lamentation or the miseries of material existence or birth and death, which are all experienced in our present life. That is the information we get from this mantra of Śrī Īśopaniṣad.