Bhashya
तान् तत्र देवान्कर्मपरान् मृत्यु यथा लोके मत्स्यघा-तको मत्स्यमुदके नातिगम्भीरे परिपश्येत् बडिशोदकस्त्रावो-पायसाध्य मन्यमान , एव पर्यपश्यत् दृष्टवान्, मृत्यु कर्म-क्षयोपायेन साध्या देवान्मेने इत्यर्थ ।कासौ देवान्ददर्शेति,उच्यते— ऋचि साम्नि यजुषि, ऋग्यजु सामसबन्धिकर्म-णीत्यर्थ ।ते नु देवा वैदिकेन कर्मणा संस्कृता शुद्धात्मानसन्त मृत्योश्चिकीर्षित विदितवन्त , विदित्वा च ते ऊर्ध्वाव्यावृत्ता कर्मभ्य ऋच साम्न यजुष ऋग्यजु सामस-बद्धात्कर्मण अभ्युत्थायेत्यर्थ ।तेन कर्मणा मृत्युभयापगमप्रति निराशा तदपास्य अमृताभयगुणमक्षर स्वर स्वरश-ब्दित प्राविशन्नेव प्रविष्टवन्त , ओंकारोपासनपरा सवृत्ता ,एव-शब्द अवधारणार्थ सन् समुच्चयप्रतिषेधार्थ , तदुपासन-परा सवृत्ता इत्यर्थ ॥
In plain words
Just as a fisherman in the world spots a fish in shallow water and knows he can catch it with a hook by draining the pool, so Death watched the gods who were absorbed in ritual actions, knowing they were within his grasp because the fruits of rituals must eventually fade. Where did Death find them? In the Rigveda, the Samaveda, and the Yajurveda—that is, in the performance of the rituals prescribed there. But those gods, purified and awakened by their practices, saw what Death was planning. Realizing this, they rose above and turned away from the rituals of the three Vedas. Despairing of finding safety in actions, they abandoned them and took refuge in the imperishable, fearless, and immortal Sound, the Om. They became entirely absorbed in meditation on Om alone. The word 'eva' (only) is used here to exclude any mixing of rituals with this path, showing that they became solely devoted to this contemplation.
Close to the Sanskrit
Just as in the world a fisherman might see a fish in shallow water, thinking it can be caught by means of a hook and draining the water, so Death watched the gods who were devoted to action, and thought they could be caught through the decay of ritual fruits. Where did he see the gods? It is said: in the Rigveda, Samaveda, and Yajurveda—meaning in the rituals associated with them. Those gods, purified and made clear-minded by Vedic rituals, realized Death's intention. Having realized it, rising above and turning away from the rituals of the Rigveda, Samaveda, and Yajurveda, and losing hope of escaping death through those actions, they abandoned them and entered the imperishable, fearless, and immortal Sound called 'Svara' (Om). They became solely devoted to the meditation on Om. The word 'eva' is used for restriction, to exclude the combination of rituals with meditation, meaning they became solely intent on that meditation.