Bhashya
ओमित्येतत् इत्यादिप्रकृतस्याक्षरस्य पुनरुपादानम् उद्गीथा-क्षराद्युपासनान्तरितत्वादन्यत्र प्रसङ्गो मा भूदित्येवमर्थम्,प्रकृतस्यैवाक्षरस्यामृताभयगुणविशेषस्योपासन विधातव्यमित्यारम्भ ।ओमित्यादि व्याख्यातम् ॥
In plain words
The syllable 'Om' is brought up again so that our focus does not wander off to other things because of intervening topics like the meditation on the Udgītha. The text begins here to prescribe the meditation upon this very same syllable, which embodies the specific qualities of immortality and fearlessness. What begins with 'Om' has already been explained.
Close to the Sanskrit
The re-taking up of the aforementioned syllable beginning with 'Om' is for the purpose that there may not be an application elsewhere, due to its being intercepted by the meditation on the Udgītha syllable and others; the commencement is with the intent that the meditation of the very same established syllable, possessing the specific qualities of immortality and fearlessness, should be ordained. 'Om' and so on has been explained.