The Isavasya Upanishad derives its name from the opening word of the text 'Isavasya' or 'Isa', meaning 'Lord' that encloses all that moves in the world. Greatly revered, this short Upanishad is often put at the beginning of the Upanishads, and marks the trend toward monotheism in the Upanishads.
Its main purpose is to teach the essential unity of God and the world, being and becoming. It is interested not so much in the Absolute in itself ('Parabrahman') as in the Absolute in relation to the world ('Paramesvara'). It says that renouncing the world and not coveting the possessions of others can bring joy. The Isha Upanishad concludes with a prayer to Surya (sun) and Agni (fire).