This Upanishad is called Isa-Vasya-Upanishad, that which gives Brahma-Vidya or knowledge of the All-pervading Deity. The dominant thought running through it is that we cannot enjoy life or realize true happiness unless we consciously "cover" all with the Omnipresent Lord. If we are not fully conscious of that which sustains our life, how can we live wisely and perform our duties? Whatever we see, movable or immovable, good or bad, it is all "That." We must not divide our conception of the universe; for in dividing it, we have only fragmentary knowledge and we thus limit ourselves.
He who sees all beings in his Self and his Self in all beings, he never suffers; because when he sees all creatures within his true Self, then jealousy, grief and hatred vanish. He alone can love. That AH-pervading One is self- effulgent, birthless, deathless, pure, untainted by sin and sorrow. Knowing this, he becomes free from the bondage of matter and transcends death. Transcending death means realizing the difference between body and Soul and identifying oneself with the Soul. When we actually behold the undecaying Soul within us and realize our true nature, we no longer identify ourself with the body which dies and we do not die with the body.
Self-knowledge has always been the theme of the Sages; and the Upanishads deal especially with the knowledge of the Self and also with the knowledge of God, because there is no difference between the Self and God. They are one and the same. That which comes out of the Infinite Whole must also be infinite; hence the Self is infinite. That is the ocean, we are the drops. So long as the drop remains separate from the ocean, it is small and weak; but when it is one with the ocean, then it has all the strength of the ocean. Similarly, so long as man believes himself to be separate from the Whole, he is helpless; but when he identifies himself with It, then he transcends all weakness and partakes of Its omnipotent qualities.