And when he mentioned the changing of the heavens and the earth, he mentioned what caused that and said: "And when the messengers..." meaning those who warned the people on that day, and they denied them. "It has been appointed..." meaning it has reached that which no one else can accomplish with the easiest matter, its appointed time which it was waiting for. It is the time of cutting off the means and the occurrence of mercy and reward for the beloved ones, and punishment and retribution for the enemies, by their testimony after gathering them upon the nations regarding what was from them of the response. And the subject of the verb in 'when' has been omitted to emphasize it, so that the soul may go in every direction regarding it. It can be understood as: what you have been promised has occurred, and you have seen from this warning what cannot be borne and cannot be established for its description by the minds. And upon that, his saying indicated what should be said: and it is.