तान्यभ्यतपत्तेभ्योऽभितप्तेभ्य ॐकारसप्रास्रवत्तद्यथा शङ्कुना सर्वाणि पर्णा-नि संतृण्णान्येवमोंकारेण सर्वा वाक्स-तृण्णोंकार एवेदं सर्वमोकार एवेदंसर्वम् ॥ ३ ॥
In plain words
He brooded upon those worlds in creative austerity, and from them, thus heated, the syllable Om flowed forth. Just as all the leaves of a tree are pierced and held together by a central pin, so is all speech pierced and held together by Om. Om is indeed all this; Om is indeed all this.
Close to the Sanskrit
He heated those [worlds]; from them being heated, the syllable Om flowed forth. That, just as all leaves are pierced through by a pin, thus all speech is pierced through by Om. Om is all this indeed, Om is all this indeed.