Bhashya
देवासुरा देवाश्च असुराश्च, देवा दीव्यतेर्द्योतनार्थस्यशास्त्रोद्भासिता इन्द्रियवृत्तय , असुरा तद्विपरीता स्वेष्वे-वासुषु विष्वग्विषयासु प्राणनक्रियासु रमणात् स्वाभाविक्यतमआत्मिका इन्द्रियवृत्तय एव, ह वै इति पूर्ववृत्तोद्भास-कौ निपातौ, यत्र यस्मिन्निमित्ते इतरेतरविषयापहारलक्षणेसयेतिरे, सपूर्वस्य यतते सङ्ग्रामाथत्वमिति, सङ्ग्राम कृतवन्तइत्यर्थः ।शास्त्रीयप्रकाशवृत्त्यभिभवनाय प्रवृत्ता स्वाभावि-क्यस्तमहरूपा इन्द्रियवृत्तय असुरा, तथा तद्विपरीताशास्त्रार्थविषयविवेकज्योतिरात्मान देवा स्वाभाविकतमो-रूपासुराभिभवनाय प्रवृत्ता इति अन्योन्याभिभवोद्भवरूपसङ्ग्राम इव, सर्वप्राणिषु प्रतिदेहं देवासुरसङ्ग्रामा अनादिका-लप्रवृत्त इत्यभिप्रायः ।स इह श्रुत्या आख्यायिकारूपेण धर्मा-इति यद्वत्, 'यदेवेदमप्रतिरूपं जिघ्रति' इति समान-प्रकरणश्रुत ॥
In plain words
The devas and the asuras: the devas derive their name from shining, representing the sense faculties illuminated by scripture. The asuras are the opposite—dark, natural impulses of the senses rooted entirely in external vital activities and sensory indulgence. The particles 'ha' and 'vai' point to ancient history. The conflict refers to that mutual usurpation where they fought, meaning they waged war. The asuras are the innate, dark-natured impulses active to suppress the light of scriptural knowledge, while the devas, whose very essence is the light of scriptural discrimination, rise to conquer those dark asuras. This mutual overpowering is like a war; the hidden meaning is that the war between devas and asuras takes place within every single living being, beginninglessly. This is presented by the scripture in the form of a narrative tale, just as in the parallel passage: 'Whatever unseemly thing this one smells.'
Close to the Sanskrit
The devas and the asuras: devas are derived from the root meaning of shining, being sense functions illuminated by scripture. Asuras are the contrary, naturally dark sense functions confined to external sense objects and vital activities due to delighting in them. 'Ha' and 'vai' are particles revealing past events. 'Where' signifies the occasion characterized by mutual plunder where they strove, meaning they waged war. The natural dark-natured asuras active to suppress scriptural light functions, and the devas whose very self is the light of scriptural discrimination active to overcome those asuras—such mutual overpowering constitutes a battle, implying that the battle between devas and asuras is beginningless in all living beings per body. This is taught here by shruti as a narrative story, just as in the parallel shruti text 'whatever unseemly thing this one smells'.