Surah 27. An-Naml, Ayah 66

I.e., they cannot truly visualize the hereafter because its reality is beyond anything that man may experience in this world: and this, it cannot be stressed often enough, is an indirect explanation of the reason why all Qur'anic references to the conditions, good or bad, of man's life after death are of necessity expressed in purely allegorical terms.

I.e., blind to its logical necessity within God's plan of creation. For, it is only on the premise of a life after death that the concept of man's moral responsibility and, hence, of God's ultimate judgment can have any meaning; and if there is no moral responsibility, there can be no question of a preceding moral choice; and if the absence of choice is taken for granted, all differentiation between right and wrong becomes utterly meaningless as well.

The Unbelievers are generally materialists, who cannot go beyond the evidence of their physical senses. As to a spiritual vision of the future, their physical senses would only leave them in doubt and uncertainty, while their rejection of the spiritual light makes them blind altogether to the next world.