John Calvin Commentary Isaiah 34:6

"The sword of Jehovah is filled with blood, it is made fat with fatness, with the blood of lambs and goats, with the fat of the kidneys of rams; for Jehovah hath a sacrifice in Bozrah, and a great slaughter in the land of Edom." — Isaiah 34:6 (ASV)

The sword of Jehovah is filled with blood. He expands on the same statement, but with a different description, which presents the matter more vividly, in order to rouse wicked men from their spiritual lethargy, who are accustomed to laugh and scoff at all doctrine, as we have previously remarked. It is therefore necessary that the judgments of God should be portrayed graphically, so that it may not only make a deep impression on their dull minds, but may also encourage believers with holy confidence, when they learn that the pride and rebellion of their enemies cannot in any way hinder them from being dragged like cattle to the slaughter, whenever it is God's will.

He compares it to sacrifices, for animals are slain in sacrifice for the worship and honor of God, and similarly, the destruction of this people will also contribute to the glory of God. Here he confirms what was previously said about judgment, for when God executes his judgments, he shows forth his glory; so that the destruction of wicked men is justly compared to “sacrifices,” which belonged to his worship.

“Sacrifices,” indeed, were undoubtedly not very pleasant and agreeable to behold, because the revolting act of taking away life, the reeking blood, and the stench of the smoke could have a repulsive effect; yet in these things the honor of God shone brightly. Thus, this slaughter was also hideous to behold and little suited to gain approval. However, believers are commanded to lift up their eyes to heaven, so that they may hallow God’s name in this respect. This is because, in executing such punishment, God erects altars to himself for slaying sacrifices. They unjustly oppressed the Church of God and, forgetful of all humane feelings, treated God’s children with cruelty. Therefore, Isaiah declares that in their blood is offered a sacrifice of sweet savor, and highly acceptable to God, because he executes his judgment.

With the blood of lambs and of goats. By this name, he metaphorically describes the people who were to be slain. Alluding to the various kinds of victims, he includes not only all men of ordinary rank but also all the nobles. This is to indicate that the Lord will punish his enemies in such a way that no one of any class whatever shall be exempt. He mentions Bozrah, the chief city and metropolis, so to speak, of the nation, where the greatest slaughter will take place. Next, he adds the country of Edom, throughout which this calamity will run its course.