Overall meaning : Allah, Exalted be He, states that He had destroyed the wicked inhabitants of many cities of past nations who worshipped other than Him and denied His messengers, such that His punishment came upon them unawares in their homes and destroyed them completely, either in the dead of night or during the midday siesta. When the scourge fell upon them, all they could do was admit they had been wrongdoers.
Then He indicates that, on the Day of Judgement, He will reprovingly ask the nations to whom He has sent His messengers whether or not they obeyed Him and followed His messengers, and He will ask those He had sent with His message concerning their duty of conveying it and how their peoples reacted to it. The Lord, who knows everything and who is fully aware of every detail, will relate to people all their words and deeds with full knowledge, for He is never unaware of anything they say or do at any time and he is witness over all things
On that day, He declares, everyone’s deeds will be weighed with absolute justice. Those whose weight of good deeds is heavy in the balance will surely be successful, but as for those whose weight of good deeds is light in the balance, in that they are outweighed by their evil deeds, they will suffer loss because of their wilful rejection of Allah’s revelations and signs.