Bhashya
यस्मादेवम् तस्मात्, एकधैव एकेनैव प्रकारेण विज्ञानघनैकरसप्रकारेण आकाशवन्निरन्तरेण अनुद्रष्टव्यम् ; यस्मात् एतद्ब्रह्म अप्रमयम् अप्रमेयम्, सर्वैकत्वात् ; अन्येन हि अन्यत् प्रमीयते ; इदं तु एकमेव, अतः अप्रमेयम् ; ध्रुवं नित्यं कूटस्थम् अविचालीत्यर्थः ।ननु विरुद्धमिदमुच्यते- अप्रमेयं ज्ञायत इति च; 'ज्ञायते' इति प्रमाणैर्मीयत इत्यर्थः, 'अप्रमेयम्' इति च तत्प्रतिषेधः- नैष दोषः, अन्यवस्तुवत् अनागमप्रमाणप्रमेयत्वप्रतिषेधार्थत्वात् ; यथा अन्यानि वस्तूनि आगमनिरपेक्षैः प्रमाणैः विषयीक्रियन्ते, न तथा एतत् आत्मतत्त्वं प्रमाणान्तरेण विषयीकर्तुं शक्यते; सर्वस्यात्मत्वे
In plain words
Since this is so, Brahman can only be seen in a single way: as the one unbroken essence of pure, massed consciousness, continuous like space itself. Because this Brahman cannot be measured, cannot be proved, since everything is one — one thing is only ever proved by something else, but this is only ever one, and that is exactly why it cannot be proved that way. It is constant, eternal, unchanging, unwavering — that is the meaning. Someone may object: isn't that a contradiction, calling it unprovable and yet saying it is known? Not really — 'is known' means it is grasped by ordinary means of knowledge, and 'unprovable' simply denies that. There is no fault here, because the whole point of that word is to rule out being provable by any means apart from scripture, exactly as with any other entity. Just as other things are turned into objects of knowledge by means independent of scripture, this reality of the self cannot be turned into an object that way by any other means of knowledge — given that everything is the self...
Close to the Sanskrit
Since it is thus, therefore, in a single way, that is, by the single mode which is the one essence of the mass of pure consciousness, continuous like space, is Brahman to be perceived; because this Brahman is unmeasurable, unprovable, on account of the oneness of all; for one thing indeed is proved by another, distinct from itself; but this is one only, therefore it is unprovable in that way. Constant, eternal, immutable, unwavering — that is the meaning. Objection: this is a contradiction that is being stated — that it is unprovable and yet is known! [Reply:] 'is known' means it is cognized by other means of valid knowledge — that is the meaning — and 'unprovable' is the negation of that; this is not a fault, because the very purpose of that word is to negate provability by a means of knowledge other than scripture, as with other entities. Just as other entities are made objects of knowledge by means of knowledge independent of scripture, not so can this reality of the self be made an object by another means of knowledge — since everything's being the self [is such that]...