The Īśopaniṣad begins with a sentence that, if taken seriously, dissolves the boundary between the sacred and the ordinary. Everything is pervaded; nothing is left out.
What follows is not a system but a series of paradoxes: act, yet do not cling; renounce, yet enjoy; the One is unmoving, yet outruns the wind.
Śaṅkara, Aurobindo and Gandhi each found a different doorway here. That a text of eighteen verses can sustain such varied commentary is itself an argument for its depth.