Bhashya
तद्ब्रह्मदर्शने साधनमुच्यते- मनसैव परमार्थज्ञानसंस्कृतेन आचार्योपदेशपूर्वकं च अनुद्रष्टव्यम् ।तत्र च दर्शनविषये ब्रह्मणि न इह नाना अस्ति किंचन किंचिदपि; असति नानात्वे, नानात्वमध्यारोपयति अविद्यया ।सः मृत्योः मरणात्, मृत्युं मरणम् आप्नोति; कोऽसौ? य इह नानेव पश्यति ।अविद्याध्यारोपणव्यतिरेकेण नास्ति परमार्थतो द्वैतमित्यर्थः ॥
In plain words
Now scripture states the means for seeing that Brahman: only with the mind, and only a mind sharpened by knowledge of the highest reality and guided beforehand by a teacher's instruction, can Brahman be perceived. And in that seeing, when it comes to Brahman, there is no multiplicity here at all, none whatsoever; it is only because multiplicity does not exist that a person can superimpose it through sheer ignorance. Whoever does this goes from death to death — and who is that? Anyone who keeps perceiving multiplicity here as though it were real. Strip away that superimposition born of ignorance, and there simply is no duality in ultimate reality. That is the meaning.
Close to the Sanskrit
Now the means for the vision of that Brahman is being stated: with the mind alone, that is, with a mind refined by the knowledge of the highest reality, and preceded by the instruction of a teacher, is Brahman to be perceived. And there, with regard to the object to be seen, in Brahman, there is not here any multiplicity whatsoever, none at all; when multiplicity does not exist, a person superimposes multiplicity through ignorance. He, from death, obtains death — who is this? Whoever perceives multiplicity, as it were, here. Apart from the superimposition caused by ignorance, duality does not exist in reality — that is the meaning.