Bhashya
रूपाण्येव यस्यायतनम् ।पूर्वे साधारणाणि रूपाण्युक्तानिइह तु प्रकाशकानि विशिष्टानि रूपाणि गृह्यन्ते ; रूपाय-तनस्य देवस्य विशेषायतनं प्रतिबिम्बाधारमादर्शादि ; तस्यका देवतेति- असुरिति होवाच ; तस्य प्रतिबिम्बाख्यस्यपुरुषस्य निष्पत्तिः असोः प्राणात् ॥
In plain words
Forms alone are his home — but not just any forms. Before, we meant colour in general; here we mean something that catches light and throws it back, a mirror, still water, anything a face can appear in. What god does this reflected person answer to? Breath, he says. Because that flicker of an image in a mirror only comes to life through the breath behind it.
Close to the Sanskrit
'Forms alone are his abode' — earlier, the forms mentioned were the general ones; here, however, particular luminous forms are meant. The special abode of the deity whose abode is form is a support for reflection — a mirror and the like. Of him, what is the deity? — 'Breath', he said; for the arising of this person called 'reflection' is from the breath.