Bhashya
मनः— मनुतेऽनेनेति ; 'पुरुषस्तु कर्ता सन्मन्वानो मन इत्युच्यते ।तान्येतानि प्राणादीनि, अस्यात्मनः कर्मनामानि, कर्मजानि नामानि कर्मनामान्येव, न तु वस्तुमात्रविषयाणि ; अतो न कृत्स्नात्मवस्त्ववद्योतकानि— एवं ह्यसावात्मा प्राणनादिक्रियया तत्तत्क्रियाजनितप्राणादिनामरूपाभ्यां व्याक्रियमाणोऽवद्योत्यमानोऽपि ।स योऽतः अस्मात्प्राणनादिक्रियासमुदायात्, एकैकं प्राणं चक्षुरिति वा विशिष्टमनुपसंहृतेतरविशिष्टक्रियात्मकम्, मनसा अयमात्मेत्युपास्ते चिन्तयति, न स वेद न स जानाति ब्रह्म ।कस्मात् ? अकृत्स्नोऽसमस्तः हि यस्मात् एष आत्मा, अस्मात्प्राणनादिसमुदायात्, अतः प्रविभक्तः, एकैकेन विशेषणेन विशिष्टः, इतरधर्मान्तरानुपसंहारात्— भवति ।यावदयमेवं वेद—‘पश्यामि’ ‘शृणोमि’ ‘स्पृशामि’ इति वा स्वभावप्रवृत्तिविशिष्टं वेद, तावदञ्जसा कृत्स्नमात्मानं न वेद ॥
In plain words
Mind is so called because one thinks with it; as scripture says, 'The person, acting and thinking, is called mind.' The faculties beginning with breath are simply functional names of this Self, names born of activity rather than indicators of its true substance. Therefore, they do not reveal the absolute, undivided reality of the Atman, even though the Self appears to be expressed through them. If someone isolates a single vital function—such as breath or the eye—and meditates on it alone as the Self, failing to integrate the whole, that person does not truly know Brahman. Why? Because that partial view makes the Self appear fragmented and incomplete, restricted to a single isolated function while ignoring all others. As long as a person understands the Self only through ordinary sensory activities—thinking 'I see,' 'I hearing,' 'I touch'—they have not yet directly known the complete and whole Atman.
Close to the Sanskrit
Mind—because one thinks by this; 'The person, being an agent and thinking, is called mind.' Those are these, beginning with breath, the name-actions of this Self, action-born names, action-names indeed, not having as their domain mere substance; therefore they do not illuminate the entire reality of the Self—thus indeed that Self, even though being manifested and illuminated by vital activities and respective name-forms produced by respective activities. He who, from this aggregate of vital activities, isolating each breath or the eye, having the nature of a particularized activity without integrating other specific activities, meditates with the mind, 'This is the Atman'—he does not know, he does not know Brahman. Why? Because this Self is incomplete, unintegrated, being separated from this aggregate of vital functions, and qualified by each single particular attribute, because of not integrating other alternative attributes. As long as this one knows thus—'I see,' 'I hear,' 'I touch,' or knows characterized by natural sensory activity, so long does he not truly know the complete Self.