He shall fly away as a dream - As a dream wholly disappears or vanishes. This comparison of man with a dream is not uncommon, and is most impressive. See Psalm 73:20; see the notes at Isaiah 29:7-8.
As a vision of the night - As when one in a dream seems to see objects which vanish when he awakes. The parallelism requires us to understand this of what appears in a dream, and not of a spectre. In our dreams we "seem" to see objects, and when we awake they vanish.

He shall fly away as a dream - Instead of rising again from corruption, as thou hast asserted, (Job 19:26), with a new body, his flesh shall rot in the earth, and his spirit be dissipated like a vapor; and, like a vision of the night, nothing shall remain but the bare impression that such a creature had once existed, but shall appear no more for ever.

He shall fly away as a dream, and shall not be found,.... Either as a dream which is forgotten, as Nebuchadnezzar's was, and cannot be recovered; or as the matter and substance of a dream, which, though remembered, is a mere illusion; as when a hungry or thirsty man dreams he eats or drinks, but, awaking, finds himself empty, and not at all refreshed; what he fancied is fled and gone (m), and indeed never had any existence but in his imagination, Isaiah 29:8;
yea, he shall be chased away as a vision of the night; either the same as a nocturnal dream, or what a man fancies he sees in his dream; or like a mere spectre or apparition, which is a mere phantom, and, when followed and pursued, vanishes and disappears; so such a man before described is chased out of the world, and is seen in it no more, see Job 18:18; the first clause, according to Sephorno, refers to the generation of the flood, and the second to the slaying of the firstborn of Egypt in the night.
(m) , Pindar. Pythia, Ode 8.

(Psalm 73:20).