यदा वा ऋचमाप्नोत्योमित्येवातिस्वरत्येवंसामैवं यजुरेष उ स्वरो यदेतदक्षरमेतदमृतमभयं तत्प्रविश्य देवा अमृता अभया अभवन् ॥ १.४.४ ॥
yadā vā ṛcamāpnotyomityevātisvaratyevaṃsāmaivaṃ yajureṣa u svaro yadetadakṣarametadamṛtamabhayaṃ tatpraviśya devā amṛtā abhayā abhavan || 1.4.4 ||
4. When people recite the Ṛk, they start with Om, reciting it with great enthusiasm. They do the same when they recite the Sāma and Yajus. This Om is akṣara and also svara. It is a symbol of immortality and fearlessness. When the gods and goddesses took refuge in it, they attained immortality and fearlessness.
Yadā vai, whenever; ṛcam āpnoti, a person recites Ṛk mantras; om iti eva atisvarati, that person recites Om with great enthusiasm; evam sāma evam yajuḥ, so also the Yajus and Sāma mantras; eṣaḥ u svaraḥ yat etat akṣaram, this akṣara [Om] is svara; etat amṛtam abhayam, this is immortal and fearless; tat praviśya, having taken shelter in it; devāḥ amṛtāḥ abhayāḥ abhavan, the gods and goddesses became immortal and fearless.
Akṣara, Om, and svara are the same. When people recite Vedic mantras, they always start with the akṣara Om. By taking refuge in Om, one attains immortality and fearlessness.