The vowel in om is pluta in the beginning of a sacred text.,
The word अभ्यादानं and means the commencement of a sacred mantra or Vedic text. Thus ओ३म् अ॒॒ग्निमीले॑ पु॒॒रोहि॑तं य॒॒ज्ञस्य॑ दे॒॒वमृ॒॒त्विजं॑ ॥ (Rig I. I. I).
Why do we say \in the beginning\? Observe ओमित्येतदक्षरमुद्गीथमुपासीत (Chhandogya Upanishad. I. 1. 1). Here ओम् is not used to indicate the commencement of a Text or Mantra, but is itself the subject of comment.,