Bhashya
दात्मविज्ञानम् ।तस्मात् विकारानृताधिकृतजीवात्मविज्ञान-निवर्तकमेव इदं वाक्यम् 'तत्त्वमसि' इति सिद्धमिति ॥
In plain words
Therefore, this statement 'that thou art' is firmly established as the sole dispeller of the deluded knowledge of a finite self bound to change and unreality.
Close to the Sanskrit
Therefore this sentence 'that thou art' is established as solely dispelling the knowledge of the individual self subject to modification and unreality.