Addressing the disbelievers in the second verse (51), it was said that the punishment of this world and that of the Hereafter was nothing but what they had earned with their own hands. Since things done usually take their shape through the work of hands, therefore, mention was made of hands. The sense is that the punishment coming to them was a direct outcome of their own deeds. And as for Allah Ta` ala, He was not the kind of authority who would bring injustice upon His servants and go about subjecting someone to punishment just for no reason.