स होवाच गार्ग्यः य एवायं यन्तं पश्चाच्छब्दोऽनूदेत्येतमेवाहं ब्रह्मोपास इति ।स होवाचाजातशत्रुः मा मैतस्मिन् संवदिष्ठाः ।असुरिति वा अहमेतमुपास इति ।स य एतमेवमुपास्ते सर्वं हैवास्मिंल्लोक आयुरेति ।नैनं पुरा कालात्प्राणो जहाति ॥२,१.१० ॥
In plain words
Gārgya said, "The sound that follows behind a man as he goes — that indeed I worship as Brahman." Ajātaśatru said to him, "Do not draw me into talk about him. I worship him as life." He who worships him thus reaches his full span of life in this world, and the breath does not leave him before his time.
The commentators
Bṛhadāraṇyakopaniṣadbhāṣyam· bhāṣya
यन्तं गच्छन्तं य एवायं शब्दः पश्चात् पृष्ठतः अनूदेति, अध्यात्मं च जीवनहेतुः प्राणः- तमेकीकृत्याह ; असुः प्राणो जीवनहेतुरिति गुणस्तस्य ; फलम्- सर्वमायुरस्मिँल्लोक एतीति- यथोपार्त्तं कर्मणा आयुः कर्मफलपरिच्छिन्नकालात् पुरा पूर्वं रोगादिभिः पीड्यमानमप्येनं प्राणो न जहाति ॥
In plain words
The sound that trails behind a walking person is united here with prana, the inner life-cause. 'Asu' (breath) as the life-cause is its defining attribute. The fruit of this meditation is that one attains his full lifespan in this world: even if afflicted by illness before his natural time, prana does not desert him.
Close to the Sanskrit
The sound which follows behind a moving, walking person—subjectively, prana is the cause of life; having unified that, he speaks. Asu is prana, the cause of life—that is its attribute. The fruit: 'he attains all lifespan in this world'—even when afflicted by diseases etc. prior to the time of life limited by the fruit of karma, prana does not abandon him.