Overall meaning :
An unbeliever mockingly demanded and called for Allah’s punishment to be hastened on him and the unbelievers, which will certainly descend upon them! None can prevent it from being meted out to them, since it will come from Allah, the Lord of exalted positions, graciousness and favours. The angels and Gabriel ascend to Him in a day whose length is fifty thousand years!
Therefore, patiently endure the idolaters’ rejection of you, Muhammad, without complaint and annoyance. The unbelievers think the punishment in the life to come impossible because they do not believe in the resurrection after death, but We see it imminent, for every future event is certainly near at hand!