एतेषु यश्चरते भ्राजमानेषु यथाकालं चाहुतयो ह्याददायन् ।तं नयन्त्येताः सूर्यस्य रश्मयो यत्र देवानां पतिरेकोऽधिवासः ॥ ५ ॥
In plain words
One who performs among these when they are blazing, offering the oblations at the proper time—these rays of the sun lead him to where the one Lord of the Devas dwells.
The commentators
Muṇḍakopaniṣadbhāṣyam· bhāṣya
एतेषु अग्निजिह्वाभेदेषु य अग्निहोत्री चरते कर्माचर त्यग्निहोत्रादिक भ्राजमानेषु दीप्यमानेषु । यथाकाल च यस्य कर्मणो य कालन्त कालमनतिक्रम्य यथाकाल यज मानम् आददायन् आददाना आहुतय त नयन्ति प्रापयन्ति । एता आहुतयो या इमा अनेन निर्वर्तिता सूर्यस्य रश्मय भूत्वा, रश्मिद्वारैरित्यर्थ । यत्र यस्मिन्स्वर्गे देवाना पति इन्द्र एक सर्वानुपरि अधि वसतीति अधिवास ॥
In plain words
Among these various tongues of fire, whoever performs sacrifices such as Agnihotra within the blazing, luminous flames—observing punctually the precise time ordained for each ritual—the oblations take up the sacrificer and carry him onward. These very offerings, performed by him and turning into the rays of the sun (meaning through the pathways of light), lead him to that heavenly realm where Indra, the sole lord of the gods, reigns supreme in his dwelling place.
Close to the Sanskrit
Among these varieties of fire tongues, the Agnihotra performer who engages in action, performing Agnihotra and others among the shining, blazing ones. And punctually, without transgressing the time which is the time of whichever action, taking up the sacrificer, the oblations lead him. These oblations which are performed by this man, having become the rays of the sun, meaning through the gateways of rays. Where, in which heaven, the lord of the gods Indra, the sole one, dwells above all, the abode.