The first verse of the Ishavaasya Upanishad is praised by Mahatma Gandhi as being the most important in all the Upanishads.
"If all the Upanishads and all the other Scriptures happened all of a sudden to be reduced to ashes, and if only the first verse in the Ishopanishad were left in the memory of the Hindu Dharmis, Sanatan Dharma would live forever" -- Mahatma Gandhi
ॐ ईशा वास्यमिदँ सर्वं यत्किञ्च जगत्यां जगत् ।
तेन त्यक्तेन भुञ्जीथा मा गृधः कस्यस्विद्धनम् ।। १ ।।
The Lord is enshrined in the hearts of all.
The Lord is the supreme Reality.
Rejoice in him through renunciation.
Covet not the wealth/possessions of others.
îsHâ vâsyamidaM sarvaM yat kiñca jagatyâM jagat,
tena tyaktena bhuñjîthâ mâ gRidhaH kasya sviddhanam. 1.
This Upanishad starts with the phrase: ‘Ishavaasyam idam sarvam’. Hence it is also known as *Ishavaasya Upanishad*. It is called the ‘*Ishopanishad*’. This forms the fortieth chapter in the vajaneya samhita of *Sukla-Yajur Veda*. Because of this reason, it is also called as the ‘*Sukla Yajur vediya samhita Upanishad*’ and as the ‘*vajasaneyi samhita Upanishad'
The rishi or the sage of this Upanishad is ‘*Datyang aadarvanar*’. His son, who is leading a normal worldly life (and not a monastic one) approaches the sage for advices on knowledge of the self. The sage, observing that his son has complete control over all the desires and that he is following all the duties and dharmas cast on him by the religious doctrines and also that he is a true aspirant of liberation and dedicated to the cause by complete surrender, teaches his son about the knowledge of the Self.