Surah 78. An-Naba, Ayah 19

Allegorically, "its mysteries will be opened to man's understanding" - thus further amplifying the concept of "the Day of Distinction between the true and the false".

A sign that the present order of things will have ceased to exist, and a new world will have come into being. Such a figure applies to the heavens in this verse and to the earth in the next verse. The mystery of what is beyond the heavens will have vanished through the doors which will then be opened. The solid mountains, as we suppose them to be, will have vanished like an unsubstantial mirage.