(So obstinate are they in rejecting the truth that) if they saw a piece of the sky falling down (on them), they would say, "This is (only) a heap of clouds!" (For they cannot conceive that it may be a punishment for their obstinate denial)
Even if they were to see a fragment from the Height falling, they would say, "A dense cloud!" (Their lack of reasoning makes them oblivious to the Law of Requital (26:187))
And (even) if they see a fragment of the sky falling down (in the form of punishment) they would say, `(It is only) piled up clouds (and not a sign of punishment whatsoever)