यत्किंचाविज्ञातं प्राणस्य तद्रूपं प्राणो ह्यविज्ञातः प्राण एनं तद्भूत्वावति ॥ १० ॥
In plain words
Whatever remains uncomprehended belongs to the form of prāṇa, for prāṇa itself is unknown. Prāṇa, becoming that very unknown reality, sustains and protects the seeker.
Close to the Sanskrit
Whatever is unknown, that is the form of prāṇa; for prāṇa is indeed unknown. Prāṇa, having become that, protects this person.