The Jews of Medina stood firmly against the propagations and preachings of the prophet, rejecting his call and message severely. They; every now and then brought another excuse for their denial; such as our hearts are covered, and we don't understand what you mean, and such and such! Of course they said that their heart was covered as an ironical utterance and in mockery; but Allah confirmed their assertion that their hearts was really covered and sealed, because Allah had cursed them for their blasphemy.