Katha Upanishad Verse 1.2.16
This verse further illuminates the power of the syllable Om. It is identified with both the manifest Brahman (Saguṇa) and the unmanifest, highest Brahman (Nirguṇa). One who meditates on and realizes the essence of this “word” attains whatever they desire, as it is the key to both worldly and spiritual fulfillment.
Sanskrit Verse
एतद्ध्येवाक्शरं ब्रह्म एतद्ध्येवाक्शरं परम् । एतद्ध्येवाक्शरं ज्ञात्वा यो यदिच्छति तस्य तत् ॥ १६ ॥
Transliteration
etaddhyevākśaraṃ brahma etaddhyevākśaraṃ param | etaddhyevākśaraṃ jñātvā yo yadicchati tasya tat || 16 ||
Translation
This word is, indeed, Brahman, this word is, in deed, the highest; whoso knows this word obtains, indeed, whatever he wishes for.

Muni's Play