“That which describes Īśvara is OM.
However OM is not mentioned as such in the Sūtra
as it is regarded as a mystic symbol given in initiation,
Because Īśvara is not like the God in Vedānta,
the word Praṇava is used to describe OM.”
– TKV Desikachar on Yoga Sūtra Chapter One verse 27

– TKV Desikachar Yoga Sūtra Study Quotes Collected and Collated
– T Krishnamacharya Yoga Sūtra Study Quotes Collected and Collated