ओमित्येतदक्षरमुद्गीथमुपासीतोमितिह्युद्गायति तस्योपव्याख्यानम् ॥ १ ॥
In plain words
Let a man meditate upon this very syllable 'Om' as the udgītha, for people chant beginning with 'Om'. Now follows its detailed explanation.
Close to the Sanskrit
One should meditate on this imperishable syllable 'Om' as the udgītha, for one chants starting with 'Om'. Here is its further explanation.