John Calvin Commentary Isaiah 15:7

"Therefore the abundance they have gotten, and that which they have laid up, shall they carry away over the brook of the willows." — Isaiah 15:7 (ASV)

Therefore what everyone has left. This corresponds to the ordinary expression, (Ce qu’il aura espargne), Whatever he shall have spared. He means the riches that are laid up, and describes what usually happens in countries that are invaded by an enemy. All the inhabitants usually convey their riches elsewhere, and lay them up in some safe place, so that they may afterward bring them back when peace has been restored.

To the brook of the willows. He means that they will have no storehouse, no fortress in which they can lay them up with safety, so that they will be compelled to hide them among the willows. This certainly is the lowest wretchedness, when the enemy is attacking us, and we can find no storehouse for laying up those things which we have collected with great industry. These willows were probably situated in some remote and sequestered place. Others explain it as referring to enemies, that they will bring the fruits of their robbery to the brook, to divide among themselves the general plunder.