अगमन्मे मनोऽन्यत्र साम्प्रतं च स्थिरीकृतम् ।एवं यो वेत्ति धीवृत्तिं सोऽहमित्यवधारय ॥ २१ ॥
In plain words
"My mind wandered off — and now it has settled." Whoever knows the intellect's movements like that: settle it firmly — I am that one.
Close to the Sanskrit
"My mind went elsewhere, and now it has been made steady" — he who thus knows the movement of the intellect, ascertain firmly: "I am that one."