In plain words
What never perishes, what the end of the Vedas makes plain by saying 'not this, not this', what abides as the one unbroken bliss: that itself is the shining Brahman. Be clear.
Word for word
Be clear that the imperishable which the end of the Vedas reveals through ‘not this, not this’, abiding as one unbroken bliss, is itself shining Brahman.