Albert Barnes Commentary Isaiah 13:7

"Therefore shall all hands be feeble, and every heart of man shall melt:" — Isaiah 13:7 (ASV)

Therefore shall all hands be faint - This is designed to denote the consternation and alarm of the people. They would be so terrified and alarmed that they would have no courage, no hope, and no power to make resistance. They would abandon their plans of defense, and give themselves up to despair (Compare to Jeremiah 50:43: The king of Babylon hath heard the report of them, and his hands waxed feeble; anguish took hold of him, and pangs as of a Women in travail; Ezekiel 7:17; Zephaniah 3:16).

And every man’s heart shall melt - Or, he will faint, so that he will have no courage or strength . The fact was, that the destruction of Babylon took place in the night. It came suddenly upon the city, while Belshazzar was at his impious feast; and the alarm was so unexpected and produced such consternation, that no defense was attempted (compare the notes at Isaiah 45:1).