كَلَّا (No): It is used as a rebuke and forbiddance of what you are engaging in out of amusement and competing in increasing the pleasures of this life as money, children, belongings and wealth until you die and be in graves. Omar Bin Abul-Aziz (may Allah have mercy on him) said: “O’ you, who shall be in grave tomorrow.., what deceived you of this life? Do you think you will remain in this life or that life will remain for you? The command from the heaven has come… The dominant destiny and fate has come.. The moment of death has come which cannot be avoided, faraway!”
Allah (swt) makes clear that it is a wrong behavior which is not a characteristic of a sensible man who thinks of the matters and arranges them normally according to their due happenings, for that Allah (swt) says (You are going to know). As if they are doubtful and are not convinced with what they see. The final recompense is presented to man in his grave, it is either the Paradise or the Hell, the grave is, as well, either as a garden of the Paradise or as a hole of the Hell fire but they are not the real Paradise or the real Hell Fire which are to be entered after the resurrection and the reckoning, only then, people will move to the stage of true certainty.