Abdullah Ibn Abbas (radi Allahu anhu) reported that the Prophet (sal Allahu alaihi wa sallam) said, “Whoever recites Surah Al Zalzalah (99) will get the reward of reciting half the Qur’an.” [Tirmidhi]
An old man, saying that his heart had difficulty in remembering, and his tongue was sluggish asked the Prophet (sal Allahu alaihi wa sallam); “Teach me the reading of a comprehensive surah.” So Rasul Allah (sal Allahu alaihi wa sallam) taught him to recite “Idha dul dilatil ardhu dhildalaha” (Surah Zalzalah) up to the end.
Why is this surah so important? If its recitation carries so much reward, it means that Allah (subhana wa ta’ala) wants us to repeatedly be reminded of its content. The theme of this surah is the life after death and presentation in it before man of the full record of the deeds done by him in this world. We are told briefly how the second life will take place and how confounding it will be for man. This very earth on which man has lived and performed all kinds of deeds thoughtlessly, and about which he never could fancy that this lifeless thing would at some time in the future bear witness to his deeds, will speak out on that Day by Allah’s command and will state in respect of each individual person what act he had committed at a particular time and place. Men on that Day, rising from their graves, will come out in their varied groups from all corners of the earth, to be shown their deeds and works, and the presentation of their deeds will be so detailed that not an atom’s weight of any good or evil act will be left hidden from anybody’s eyes.
It might have been difficult for a man of ancient times to understand how the earth will speak and narrate the annals and events happening on it on the Day of Resurrection, but in the present age of the inventions of the cinema, loudspeaker, radio, television, tape-recorder, electronic equipment, etc., it is no longer difficult to understand how the earth will narrate its annals. The impression of whatever man speaks is preserved in the air, in the radio waves, on the particles of the walls and floors and ceilings of the houses, and on the environments of the road, plain or field if he spoke outside the house. If Allah so wills He can make these things repeat all these voices precisely in the way these were uttered in the first instance by man. Man at that time will hear with his ears and know that it was his own voice, and all his acquaintances also will testify that whatever they were hearing was the person’s own voice and his own accent. Whatever man has done anywhere on the earth, and in whatever state, has had its impression on everything of the environment and its image inscribed on it. Even if he did something in pitch darkness, there are such rays in the Kingdom of God for which darkness and light make no difference; they can preserve his image in any case. All these images will pass before man on the Day of Resurrection like a motion picture, and will show him when and where he had done something during his life on earth.(Tafhim al-Quran, Sayyid Abul Ala Maududi)