Om.  That Supreme Brahman is infinite,  and this conditioned Brahman is infinite.  The infinite proceeds from infinite.  Then through knowledge,  realizing the infinitude of infinite,  it remains as the Infinite alone.

Isha Upanishad or Ishavasyopanishad is one of the principal Upanishads consisting of only eighteen verses, but of immense significance. The deep meaning contained in each verse is highlighted by many a commentator, notably Shankaracharya.

Isha Upanishad derives its name from the opening words of the first verse, 'Isha vasyam' The subject matter of the Upanishad, as of all the Upanishads, is spiritual, profound, and all comprehensive. It forms the foundation of Vedantic System of thought. It highlights the divinity of man, as well as all manifestations in nature. It tries to convey to us the knowledge of the seers who have had experienced the spiritual solidarity and unity of all existence.

Verse 1.

Om. All this, whatever moves on the earth, should be covered by the Lord. Protect your Self through that detachment. Do not covet anybody's wealth. Or - Do not covet, for whose is wealth? 1

Everything in this universe is transitory and therefore, can be labeled as relatively real, or temporarily real, or illusory. This is the meaning of 'whatever moves on the earth'. Then all these things -everything one sees, feels, thinks, or imagines - in short the whole universe 'should be covered with the Lord'. Who is this Lord? The Lord is none other than our indwelling Self. Know this and try to see the same Self manifest in all 'things in motion' on this earth. In other words, renounce everything that is not your Self; or know that the essence of universe is your true self. In either case, there are no two; the only reality or truth is one Self. Knowing this the realized soul renounces this illusory world of name and form and becomes free from threefold desire, viz. son, wealth, and worlds. Thus, 'protect your Self' through such detachment and realize your true nature through the knowledge obtained through discrimination and renunciation.

The world is not to be abandoned, but is to be defied as one divine Self. Attachment to the wealth in any form is to be sublimated by realization that all the wealth is illusory and the real Lord is our indwelling Self in everything.

This first verse is meant for those who are fit to renounce threefold desire through knowledge. But for those who are unable to grasp this higher knowledge because of involvement in the non-self -worldly attachments - the second verse imparts the instruction.

Verse 2.

'By doing karma, indeed, should one wish to live here for a hundred years. For a man, such as you (who wants to live thus), there is no way other from this, whereby karma may not cling to you. 2

The person who has had not yet attained to the right knowledge should lead the life engaging in such karma (work, actions) that are enjoined by the Vedas. [Sri Krishna in the Gita elaborating on this point says that such a person should perform such actions as are suitable to his nature.] As most of us have not been as yet able to separate our consciousness from its human entanglement, therefore, such karmas would help us to sharpen our faculties of reason and discrimination, and thereby purifying our minds.

Shankaracharya maintains that all the activities - work - springs forth as a result of overt or latent desires, and thus form the antithesis of Freedom, the absolute desire-less state. Thus, actions and knowledge cannot go together. Hence, two paths emerged based on

1) Those persons who give up all the karmas and retire to the forest, and 
2) The others who desire to live for hundred years and carry out karma in this world.

Of these, the path of renunciation - detachment - is excellent. The other path of karma is based on attachment and ignorance, and progressively tries to show the aspirant difficulties and limitations in it. In the final analysis a state is reached when through discrimination and renunciation even the karma yogi would attain to the highest knowledge - Jnana.

Those worlds of devils are covered by blinding darkness. Those people that kill the Self go to them after giving up this body. - Verse 3

Those states in which the results of karma are perceived or enjoyed are in fact the states of darkness, characterized by ignorance. This ignorance/lack of knowledge impels such persons to take repeated births in accordance with their karma. In such persons the shining Self remains concealed, as if killed, under the clouds ignorance.

Verse 4, 5, and 8 describe the nature of Self as:

It is unmoving, one, and faster than the mind. The senses cannot overtake It, since It is already there where and when min tries to reach. Only all pervasive, stationary, and infinite entity (Absolute Consciousness) can qualify to become the Self. Only such Self can be described as, "That moves, that does not move; that is far off, that is very near; that is inside all this, and that is also outside all this."

Verse 6. 7.

The sadhaka, who sees all beings in the Self, and the self in all beings, feels no hatred by virtue of such realization. There is neither sorrow nor delusion for that seer of Oneness. The Gita (Chapter XI, verse 29, 30, 31 etc.) one finds similar echo of truth.

Verse 9. 10. 11.

These verses describe empirical knowledge as 1) Vidya and 2) Avidya. Here the word knowledge should be seen as worldly knowledge, for both Vidya and Avidya blind and delude the person from true reality. Both should be transcended to reach the highest state of Knowledge.

Theoretical grasp about Self without sincere and honest efforts to realize the Self is called Vidya, while to take delusory experiences perceived through the senses as true constitutes Avidya. Avidya knowledge binds the people more and more to the illusory world. Through Avidya a person never comes to realize that he/she has to go further! Such people are termed as 'bound souls'. Their only chance then remains to associate with holy company and serve the men of realization whereby the darkness of ignorance can be removed at least bit-by-bit. Most of us are thus ignorant about the truth of higher knowledge. An illumined person tries to help us when out of love he elaborates the concepts of Truth etc.

Vidya knowledge might lead a person towards realizing the goal, but the people under the veil of Vidya Maya are difficult to convince about the nature of their ignorance. For, just by reading, hearing, or reasoning about the Truth they think and are convinced that they have realized the Self! Under this false sense of achievement they go on teaching and telling others, and also start behaving as if they have realized the Truth. These people without applying themselves to austerities, tapas, renunciation, and spiritual practices delude themselves and harm others as well. Therefore, it is said that those who pride themselves under the influence of Vidya knowledge actually are pushed more and more into the darkness of ignorance.

Therefore, it is said, "He who knows these two - both Vidya and Avidya together - attains immortality by transcending them - Verse 11.

Verse 15. 16. 17. 18. 

In the concluding Verses the Upanishadic seer, out of compassion and love for all, prays to the Lord to reveal His true nature. For example:

"The face of Truth is concealed by a golden vessel. Do thou, O Sun, open it so as to be seen by me who am by nature truthful (or, am the performer of rightful duties)." Verse 15 - Sri Ramakrishna tried to explain the meaning of these verses somewhat like this:

O gracious Lord, you are holding the lamp in your hand. Although the light from it is spreading all around and illumining whole external world, I am unable to see your face. My senses are being drawn to the outside objects in this illusory world but are unable to fathom the true nature of the Lamp Holder! I am able to see the magic of the magician, but unable to recognize the Magician. O kind One, for once heed my prayer and turn the focus on Your Face so that I may have a glimpse of Your true Nature in the light of Your illumining Grace.