Albert Barnes Commentary Isaiah 16:9

"Therefore I will weep with the weeping of Jazer for the vine of Sibmah; I will water thee with my tears, O Heshbon, and Elealeh: for upon thy summer fruits and upon thy harvest the [battle] shout is fallen." — Isaiah 16:9 (ASV)

Therefore, I will bewail, — So great is the desolation that I, the prophet, will lament it, though it belongs to another nation than my own. The expression indicates that the calamity will be great (see the note at Isaiah 15:5).

With the weeping of Jazer — That is, I will pour out the same lamentation for the vine of Sibmah as I do for Jazer, implying that it would be deep and bitter sorrow .

I will water you with my tears — This indicates the grievous calamities that were coming upon those places, on account of the pride of the nation. They were foreign nations to Isaiah, but he had a heart that could feel for their calamities.

For the shouting for your summer fruits — This refers to the shouting attending the ingathering of the harvest (note, Isaiah 9:3). The word used here (הידד hēydâd), properly denotes a joyful acclamation, a shout of joy or rejoicing, such as was manifested by the vintager and presser of grapes (Jeremiah 25:30; Jeremiah 48:33), or such as was made by the warrior (Jeremiah 51:14).

In this context, it means that at the time when they would expect the usual shout of the harvest, it will not be heard; instead, there will be the triumph of the warrior. Literally, ‘upon your summer fruits, and upon your harvests has the shouting fallen;’ that is, the shout of the warrior has fallen upon that harvest instead of the rejoicing of the farmer.

Jeremiah evidently understands it this way (Jeremiah 48:32): The spoiler is fallen upon thy summer fruits, and upon thy vintage. Lowth proposes a correction of the Hebrew text here, but without necessity or authority.