I find this passage one of the most confusing in the entire book. The harvest language, though initially a little gruesome, actually makes more sense once you realize that harvest time was a joyful occasion for agrarian societies.
But the winepress was almost always the language of bloody, violent, judgment in the First Testament. And I feel uncomfortable with the thought that Christ might here be employing the methodology of the Beast in order to bring about his Kingdom Come.
A couple of textual notes—courtesy of Darryl Johnson, George Caird, FF Bruce, and NT Wright—have helped me find my way through, albeit slowly
For starters, in the First Testament “the vine of the earth” referred to Israel. But Jesus expropriated the term first for himself (“I am the True Vine…”) and then for his followers (“…and you are the branches.”). When John records the angel gathering the fruit from the vine of the earth, he’s referring to the blood of Christ—which cleanses sin—and the blood of the martyrs—who followed Jesus and died as a result.
“Outside the city” is also an important phrase, given that it was an early Christian means of referencing the cross (see Hebrews 13.12-13, for example, “therefore Jesus…suffered outside the city gate…”). Salvation came from “outside the city” via the cross. The winepress of God’s anger outside the city gate, then, is the cross. That is where God’s wrath was fully expressed against the contamination of sin (see Romans 3.21-26).
The “blood that flows up to the horses bridle for about 200 miles” becomes clearer when we understand that 200 miles was originally rendered 1600 stadia. 1600 refers to two things simultaneously. First, its the traditional length of Palestine in the ancient world, meaning there’s “blood enough” for those who rejected Christ. Second, 1600 is 40×40, where 4 = the number of creation and 10 = the number of the multitudes, meaning there’s “blood enough” for all creation.
And whose blood is it? The blood of God’s enemies?
No—it’s the blood of Jesus, the vine of the earth, and of his followers who were killed in his name. God spilled his own blood to save the world. This passage is less about God blowing up his enemies and dancing on their graves, than about the final reconciliation between Creator and Creation at His own expense.