Bhashya
यदा वै ऋचम् आप्रोति ओमित्येवातिस्वरति एव सामएव यजु , एष उ स्वर , कोऽसौ ? यदेतदक्षरम् एतदमृ-तम् अभयम्, तत्प्रविश्य यथागुणमेव अमृता अभयाश्चअभवन् देवा ॥
In plain words
When someone reaches the Ṛc and chants aloud with 'Om'—the Sāman itself, the Yajus, the very tone—what is that tone? It is this imperishable, immortal, fearless syllable. Entering it, the gods became immortal and fearless, each according to their measure.
Close to the Sanskrit
When indeed one attains the Ṛc, chanting aloud precisely with 'Om', the Sāman itself, the Yajus, this verily is the tone,—which is that? That which is this imperishable, this immortal, fearless one; having entered that, according to their quality indeed, the gods became immortal and fearless.