The phrase "and on their eyes is a veil (wa 'alâ absârihim ghishâwatun)" alludes to the loss of a huge bounty in consequence of their unbelief. For when the eye is illuminated with the light of belief dwelling behind its pupil, the light assists and impels it, and the whole universe becomes a garden for it bedecked with flowers and houris. The eye's pupil becomes a bee, flying hither and thither gathering from the blooms the juices of reflection, thought, familiarity, friendliness, love, and felicitation. It takes up its load, which in the conscience is transformed into the honey of perfections.
But if, God forbid!, the eye becomes dimmed and lustreless through disbelief, the world becomes a prison in its view, its truths are hidden from it, and the universe becomes a wasteland, causing such pain to the heart that it overwhelms the conscience completely.
Moreover, with the phrase "great is the penalty they incur (wa la-hum 'adhâbun 'azîm)" it indicates a fruit of the Zaqqum-tree of unbelief in the next world, which is the torment of Hell and the terrible punishment of divine wrath.
While "they will not believe (lâ yu'minûn)" corroborates "the same (sawâ'un)," explicating the manner of the sameness.