Overall meaning : When the sky is split asunder on Resurrection Day, thus listening to and obeying its Lord in true submission, and it must listen to and obey His command; when the earth is levelled out, becoming a vast even surface without any elevations or depressions, and casts forth all the dead within it to its surface, thus listening to and obeying its Lord in true submission; and it must listen to and obey His command: When such horrifying events take place, every person will know for certain what good or evil deeds he has done in the life of the world.
O man, you are striving hard and toiling on towards your Lord, whom you will inevitably meet with your work, and He will repay you according to your deeds.