Charles Ellicott Commentary Isaiah 51:6

"Lift up your eyes to the heavens, and look upon the earth beneath; for the heavens shall vanish away like smoke, and the earth shall wax old like a garment; and they that dwell therein shall die in like manner: but my salvation shall be for ever, and my righteousness shall not be abolished." — Isaiah 51:6 (ASV)

Shall die in like manner — that is, they shall vanish into nothingness. Many commentators, however, render it as shall die like gnats; they shall live their little day and pass away, thus supplying a third comparison, in addition to the “smoke” and the “garment.” We are reminded once again of Psalm 102:26; and we may add Matthew 24:35; 2 Peter 3:10.