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40th Chapter of Yajurved is source of all Upanishad and also known as Ishopnishad (Isha Upanishad). One will get benefit of studying Ved & Upanishad by studying the Isha Upanishad. Every one should read the Ishopnishad. This Upanishad has only 18 Mantra, however, it is so full of knowledge that it has first position among all eleven Upnishad.