(On the day when it befalleth in earnest) a matter to which they were blind in the life of the world; it is also said this means: when a severe, horrific matter is revealed; and it is also said that this means: when a sign between them and their Lord is revealed, (and they are ordered to prostrate themselves) this is because they said: By Allah, our Lord, we were not idolaters or hypocrites (but are not able) to prostrate, their bodies remaining erect like solid fortresses,