This Upanishad desires its title from the opening words Isa-vasya, "God-covered." The use of Isa (Lord)—a more personal name of the Supreme Being than Brahman, Atman or Self, the names usually found in the Upanishads—constitutes one of its peculiarities. It forms the closing chapter of the Yajur-Veda, known as Shukla (White).
Oneness of the Soul and God, and the value of both faith and works as means of ultimate attainment are the leading themes of this Upanishad. The general teaching of the Upanishads is that works alone, even the highest, can bring only temporary happiness and must inevitably bind a man unless through them he gains knowledge of his real Self. To help him acquire this knowledge is the aim of this and all Upanishads.
Isa-Upanishad
Peace Chant
OM! That (the Invisible-Absolute) is whole; whole is this (the visible phenomenal); from the Invisible Whole comes forth the visible whole. Though the visible whole has come out from that Invisible Whole, yet the Whole remains unaltered.
OM! PEACE! PEACE! PEACE!
The indefinite term "That" is used in the Upanishads to designate the Invisible-Absolute, because no word or name can fully define It. A finite object, like a table or a tree, can be defined; but God, who is infinite and unbounded, cannot be expressed by finite language. Therefore the Rishis or Divine Seers, desirous not to limit the Unlimited, chose the indefinite term "That" to designate the Absolute.
In the light of true wisdom the phenomenal and the Absolute are inseparable. All existence is in the Absolute; and whatever exists, must exist in It; hence all manifestation is merely a modification of the One Supreme Whole, and neither increases nor diminishes It. The Whole therefore remains unaltered.