Overall meaning : When the stars lose their light, the sky is split open, the mountains crumble into dust and Allah’s messengers are brought together at the appointed time, what you, people, have been promised will then come to pass.
For what day has the coming together of the messengers been postponed? For the Day of Decision, on which Allah will judge and decide between people. What will make you know what the Day of Decision is, Muhammad?!?
Woe betide, on the Day of Resurrection, those who deny the truth!