आत्मा नियामकश्चान्तर्देहो बाह्यो नियम्यकः ।तयोरैक्यं प्रपश्यन्ति किमज्ञानमतः परम् ॥ १८ ॥
In plain words
The Self is inside, and it does the governing. The body is outside, and it is what gets governed. Yet people look at these two and see one thing. What ignorance goes deeper than that?
Close to the Sanskrit
The Self is the controller and is within; the body is outer and is that which is controlled. Of those two they see oneness — what ignorance is greater than this?