The unconditioned Brahman is free from the limiting adjuncts of space, time and causation. Brahman is not born, It does not die. Brahman is unknown and unknowable. To be known, a thing must be made an object. Brahman as pure consciousness, is the eternal subject, and therefore cannot be made an object of knowledge.
Pure existence is the same as pure knowledge and pure bliss.
Just as a mirage could not be seen without the desert, which is its unrelated substratum, so also the universe could not be seen if Brahman did not exist as its substratum.