John Calvin Commentary Isaiah 15:4

"And Heshbon crieth out, and Elealeh; their voice is heard even unto Jahaz: therefore the armed men of Moab cry aloud; his soul trembleth within him." — Isaiah 15:4 (ASV)

And Heshbon shall cry, and Elealeh. Here he names other cities, for his design is to bind up, as it were, in a bundle all the cities of that country, so that they may be involved in the general destruction, as if he had said that none at all will be exempted.

Therefore the light-armed soldiers of Moab shall howl. Though על כן (gnal ken) literally signifies therefore, yet some think that a reason is not here assigned; but that is of little importance. The Prophet shows that there will be no one who does not howl; for he declares that the bold and courageous will mourn. Next he adds, the soul of every one shall howl to him. Everyone will be so engrossed with his own grief that he will not think of his neighbors.