स होवाच गार्ग्यः य एवायमादर्शे पुरुष एतमेवाहं ब्रह्मोपास इति ।स होवाचाजातशत्रुः मा मैतस्मिन् संवदिष्ठाः ।रोचिष्णुरिति वा अहमेतमुपास इति ।स य एतमेवमुपास्ते रोचिष्णुर्ह भवति ।रोचिष्णुर्हास्य प्रजा भवति ।अथो यैः संनिगच्छति ।सर्वांस्तानतिरोचते ॥बृह. २,१.९ ॥
In plain words
Gārgya said, "The person who is in a mirror — him indeed I worship as Brahman." Ajātaśatru said to him, "Do not draw me into talk about him. I worship him as the shining one." He who worships him thus becomes shining, and his offspring become shining; and he outshines all those with whom he comes together.
The commentators
Bṛhadāraṇyakopaniṣadbhāṣyam· bhāṣya
आदर्शे प्रसादस्वभावे चान्यत्र खङ्गादौ, हार्दे च सत्त्व- शुद्धिस्वाभाव्ये च एका देवता; तस्या विशेषणम्- रोचि- ष्णुः दीप्तिस्वभावः; फलं च तदेव, रोचनाधारबाहुल्या- त्फलबाहुल्यम् ॥
In plain words
Whether in a clear mirror or similar surfaces like a polished sword, or within the heart and the natural clarity of a purified mind, the deity is one. Its characteristic attribute is radiant light, and the fruit is that very light itself—the multiplication of results comes simply from the multiplicity of its supports.
Close to the Sanskrit
In a mirror, and in a nature of clarity, elsewhere in a sword etc., and in the heart, and in the inherent nature of mind-purity, there is one deity; its attribute is shining, of luminous nature; and the fruit is that very same one, from the abundance of luminous supports comes the abundance of fruit.