Overall meaning : Allah Almighty says: If you could only see the unbelievers when they are seized with terror upon seeing Allah’s punishment! There will be no escape for them, and they will be seized from a nearby place.
They will say upon seeing their evil fate, ‘We now believe the truth!’ But how can they possibly reach and accept the truth from a place so far-off from the worldly life (that is, the hereafter), seeing that they rejected it before, and they used to cast scorn on the truth from a place equally far away from life hereafter (that is, the worldly life).
A barrier will be set between them and what they desire, just as was done with the unbelievers of the past nations who behaved like them. They were all in disquieting doubt of the hereafter ever taking place.