كَلَّا سَيَعْلَمُونَ ثُمَّ كَلَّا سَيَعْلَمُونَ (Truly, they will soon know. Again, truly, they will soon know....78:5) The particle kalla is negative, and means 'never, by no means'. It means here that this matter cannot be understood by question and answer or by disputation and debate. Its reality will be understood by them when they will face it. It is such a reality that has no room for questions, disputation or denial. The Qur'an says that soon they will come to know about it [ and this statement is repeated twice for emphasis ]. In other words, when they die, they will discover the realities of the next world. They will see the horrors of the Hereafter with their eyes.
Then the Holy Qur'an has pointed to different demonstrations of His power to prove that it is not impossible for Allah to destroy this entire world and re-create it once again. Reference is made to the creation of earth, mountains, human beings, males and females and the creation of suitable conditions for human life, health and activities. One of the things mentioned in this connection is: