God's vengeance is a terrible thing to behold. Once again, it is essential to understand several points: (1) the divine wrath is never capricious, never directed against the nations and foreigners simply because they are other, but only because they oppose God's saving work and God's liberation of the oppressed; (2) this total destruction uses the Divine Warrior image of Canaanite mythology; it is symbolic language, not documentary history; (3) with images like the rotting away of the heavens and the rolling up of the skies (34:4), this material crosses from prophecy into the realm of apocalyptic (like the book of Revelation); it symbolically describes the final battle against evil, when all things are put right and God rules supreme; it does not describe real or desired warfare in the present age.
Nevertheless, the text does make clear God's enduring anger against everything that opposes God's work in the world. God will respond in different ways, including the long-suffering and patient waiting for the conversion of the wicked (Exodus 34:6; Matthew 13:24-30; Romans 2:4); this final cataclysmic battle is a symbolic depiction of the overcoming of evil itself in God's own future.
Edom is taken symbolically as a representative of evil--that which stands in the way of God--because historical Edom stood in the way of the Israelites on their wilderness journey toward the promised land (Numbers 20:14-21).
The Divine Warrior image, a common theme of Canaanite mythology, is taken over frequently by Israel when the issue is Good and Evil itself, when a particular event or battle is seen to have cosmic significance. It is used, for example, in Moses' song after the exodus (Exodus 15:3) and several other times in Isaiah (see 59:15b-19 and especially 63:1-6, the text from which the Battle Hymn of the Republic takes the image of "trampling out the vintage where the grapes of wrath are stored").
Pictures of the Divine Warrior sometimes include descriptions of the symbolic armor of God (59:17), which in the New Testament is given to believers to protect them against "the wiles of the devil" (Ephesians 6:11-17).
Chapters 34 and 35 mark the end of the first part of the book of Isaiah, and together they look forward to what is to come, describing God's great transformation--the total judgment of the wicked (chapter 34) and the final salvation of the faithful (chapter 35).
5 When my sword has drunk its fill in the heavens,
lo, it will descend upon Edom,
upon the people I have doomed to judgement.
6 The Lord has a sword; it is sated with blood,
it is gorged with fat,
with the blood of lambs and goats,
with the fat of the kidneys of rams.
For the Lord has a sacrifice in Bozrah,
a great slaughter in the land of Edom.
7 Wild oxen shall fall with them,
and young steers with the mighty bulls.
Their land shall be soaked with blood,
and their soil made rich with fat.
New Revised Standard Version Bible: Anglicized Edition, copyright © 1989, 1995 National Council of the Churches of Christ in the United States of America. Used by permission. All rights reserved worldwide. http://nrsvbibles.org