What does the gathering of grapes into the wine vat represent?
It represents God sovereignly gathering the military people into Israel's valleys—especially the Valley of Esdraelon and the Jordan Valley—where they are packed together to be crushed by the presence of God as the great winepress of His wrath.
Les explains that the gathering of grapes into the wine vat represents the gathering of these military people into the Valley of Esdraelon, down the Jordan Valley, and into all the low-lying areas of Israel especially. They are going to be packed in like sardines in a can—contrary to good military operation—but they will be forced by a sovereign God to pack their men into these valleys. That is the wine vat, like putting grapes in the vat. The very presence of God will then come and crush them as grapes in the vat. In verse 19, the angel thrust in his sickle into the earth and gathered the vine; all their armies will be brought to the Middle East and cast into the great wine press of the wrath of God. Les also notes God's wrath is not being poured out tonight, and we have no idea what the wrath of God will do; even floods, earthquakes, and volcanoes are nothing compared to what it will be when the wrath of God is finally released.
And the angel thrust in his sickle into the earth, and gathered the vine of the earth, and cast it into the great winepress of the wrath of God.