The first two lines of Ishavasya Upanishad are the Shanti Mantras, or the mystic syllables of peace. It is a tradition that an Upanishad begins and ends with a mantra called Shanti Mantra. The meaning of this mantra is wonderful.
Om purnamadah purnamidam purnat purnamudachyate,
purnasya purnamadaya purnameva avashishyate.
Om Shantih Shantih Shantih
That is full, this full. From the full, the full is taken, the full has come. If you take the full from the full, the full alone remains.
It can be said again in this manner: "This is one and that is one. From one the one has come, and if from one you take out one, one alone remains."
The mathematical equation of this mantra would be: "One minus one is equal to one." How?
The word purna needs a detailed commentary. Purna means 'full'. Literally, purna means 'complete'. Philosophically, purna means 'infinite', because nothing else but infinite can be full. Infinity is something of which the beginning and the end cannot be determined. It is ananta and it is akhanda. Ananta, endless and akhanda, partless, divisionless, fractionless.
If you think about the cosmos, or this great universe, about which much has been spoken and yet much remains to be known, you will realize that there seems to be two states or forms of existence. One form of existence is that which is visible. It is called the manifest universe, or the vyakta, it is the manifested form of the universe, which is seen, known, recognized, and which can be discovered, in the far and near future. The other form of existence is unmanifest, invisible and unknown to us. So, there are two types of universe: the manifest and the unmanifest.
One cosmos or universe is visible to me, to you and to the scientists. Maybe, in the far future, they will be able to know many more things. The endless galaxies of stars, the Milky Way, and the hundreds 'and thousands of solar systems in addition to our own solar system which exist millions and billions of light years away from here, constitute our universe.
That universe which has become manifest and has materialized in a shape, form, pattern or substance, like Earth, Sun, Moon, Pluto, Neptune, and that which has evolved to a particular stage, is spoken of in this mantra, by the word idam, which means, 'this manifested universe'.
In addition to this universe, which is visible, recognizable and discoverable, there seems to be, and should be another part of the universe, which is called avyakta, or the unmanifest. Indian philosophy gives a lot of reference to this aspect of reality, that there ought to be a face to the universe which is unmanifest. Even as a number of seeds are sown in your garden, a few come up and it remains to be said: "Well, a few seeds are still there," so the universe which has not come up, but which is still in the bosom of the infinite, is indicated by the word adaha 'the unmanifest universe'.
That unmanifest universe which has not taken a shape, and is lying hidden in the darkness of nature, is infinite. It is not a limited thing. That unmanifest universe is not a thing of limited dimensions. The cosmos also appears to be infinite. From that infinite universe, this finite universe has come up. All that we see is an evolved form of that unevolved and unmanifest reality, which is yet to come.
The usual mathematical law prescribes: one minus one is equal to zero. What is already obvious and clear, both to our eyes and the mind, is this manifest universe, which has come out from that unmanifest stage of the universe, uniquely supreme in its quality of oneness and singleness, unmatched and unequalled in its true and real unity. Evidently when we think and talk of the manifest unity of infinite dimensions, which is part and parcel of the unmanifest, unity, also of infinite dimensions, it is not a matter of deduction but purely an issue of manifestation. But, please understand more fully the meaning of the word 'infinite'.
When you say infinite, you postulate something which has no beginning and no end. Therefore, it only means that this manifest universe is only an extension of that unmanifest essence or reality of Creation. Therefore, this mantra says that if this universe is an outcome of that manifest prakriti, then the unmanifest remains unaffected, unchanged and unaltered. This is the literal meaning of this mantra.
Now, let me give a very simple meaning of this. In fact, in Vedanta and in the Upanishads, we believe that anything you see in the universe is not everything. It is the immanent aspect of a Supreme Power, and to a Vedantin, who is the seeker of knowledge, the existence of God cannot be proved and spoken of in terms of theology and mythology.
If the God of a bhakta is theriomorphic or anthropomorphic, like Hindu and Greek Gods, then the God of a Vedantin is the manifest and the unmanifest infinite universe. We must understand that a true Vedantin believes in an infinite, formless, all-pervading and eternal essence of reality. He does not believe in a God who is subjected and conditioned by time and limitations of the mind. A Vedantin, a seeker of Truth, does not believe in a God who is subject to your visions, fancies and imaginations. The search of a Vedantin starts with a belief that there is an eternal and infinite reality.
There are two sources by which you can know the Truth. One is to go on negating the Truth; and the other is to accept the Truth as infinite. There have been people who negated the Truth in order to know it. They denied the existence of an eternal reality. In the wisdom of the great philosopher Descartes, every negation becomes a positive assertion of reality. The more he denies reality, the more he logically affirms it. To negate the existence of a thing is one approach. This approach is only for great thinkers and not for cowards. To deny the Truth and the reality needs courage and bravery. People are afraid to deny God, because they think, if they deny God, God will punish them. But, brave people, who go in search of reality, do not accept God hypothetically. They deny Him first, and as a result of that they understand God, if there is any, in the most true form. They are not hypnotized by the statements made by a few half-baked thinkers. They say, "No, we do not accept anything which is superficial." And that is one approach, this is the approach of an atheist. The meaning of atheism in the West is different. In Indian philosophy, atheism is one of the ways of the quest of reality.
The second approach is, to accept that there should be something, otherwise there could not exist law, order and a system. That combines ontological, teleological and cosmological evidence, by observing timely recurrence of seasons and witnessing the definite laws in the operation of nature. It seems that a few sincere thinkers started the quest for Truth, but ultimately they could not arrive at the point that is God, and they got lost in the darkness. They went ahead in search of Truth and there came a certain stage where they began to cry out, 'Oh! I am the Truth; I am the Truth.' They were lost in the Truth, and they became Truth itself. This is the process and the theme, which the Upanishads have picked up.
Throughout the Upanishads one finds that there is a search for the ultimate knowledge. There is a quest for the Ultimate and the Truth, for the eternal, infinite and the Unchangeable Being. Ishavasya is only one of the Upanishads. There are many hundreds more. In all the Upanishads, you may find that God is not accepted in toto.
The words 'God' in English, and 'Paramatma' in Sanskrit, are inadequate. Therefore, the Vedantins prefer to call Him Brahman, Purnam, Advaita and Atman. Because, it is true that in this universe there cannot be one single God, and if there is one single God, He cannot be a small or limited God. He must be infinite and eternal. And if He is infinite and eternal, how can our limited and finite mind understand Him?
So sometimes by reading the Upanishads one develops scepticism for the time being. Upanishads are easily understood by one who practises integral yoga, combining karma, bhakti, raja and jnana yogas together. If one practises the truth of the Upanishads with yoga, knowledge comes to him without any confusion.