For my sword has drunk its fill in the heavens: The Hebrew particle ki rendered For may be a logical connector or an emphatic marker here (see the comments below). My sword has drunk its fill in the heavens is a metaphor for God completing his judgment/punishment of the heavenly bodies. In Hebrew a sword has a “mouth,” so it can drink blood (see verse 6). Has drunk its fill means the sword has drunk enough, and is unable to drink any more. The heavens refers to the sky, not the heavenly home of God. It renders the same Hebrew word as “heaven” and “the skies” in the previous verse. For languages that have difficulty with the metaphor here, this line may be rendered “My sword of judgment/punishment has completed its work in the sky/heavens” or “My punishment of the sky is completed.”

Instead of my sword has drunk its fill in the heavens, which follows Masoretic Text, one Dead Sea Scrolls text reads “my sword appears in the heavens.” Revised English Bible follows this reading with “my sword appears in heaven” (similarly Bible en français courant). Good News Translation may be rendering it also with “The LORD has prepared his sword in heaven” (similarly Die Bibel im heutigen Deutsch). The Hebrew Old Testament Text Project committee is divided in its opinion on whether to follow Masoretic Text or Dead Sea Scrolls here. We prefer the Dead Sea Scrolls text (see the third example below), especially for languages that need to provide an object for the verb “drink,” but translators may follow either one. Whichever text they follow, they should add a footnote giving the alternative. If they follow Masoretic Text, then the Hebrew particle ki rendered For is probably a logical connector. It gives the reason for the punishment mentioned in the next two lines: because God has completed his punishment of the heavenly bodies, he will now punish the Edomites, who represent all the nations. If translators follow Dead Sea Scrolls, this particle is probably an emphatic marker, which may be rendered “Truly” or “Indeed.” It may be left implied in either reading.

Behold, it descends for judgment upon Edom, upon the people I have doomed: Yahweh’s sword of judgment is about to come down on the Edomites. The word behold calls attention to this impending judgment. For Edom see 11.14. The Edomites were descendants of Jacob’s brother Esau (see Gen 25.30). They were often in conflict with the people of Judah. When the Babylonians captured and destroyed Jerusalem, the Edomites assisted them. This added greatly to the ill feelings between Judah and Edom (see Psa 137; Jer 49.7-22; Oba 1-21). Here the prophet speaks of the punishment that will come on Edom for that reason. The people I have doomed means Yahweh has decided to destroy the Edomites completely as a sacrifice. New Jerusalem Bible says “the people vowed to destruction.” For doomed see Isa 34.2.

There is another textual problem in this verse, but it is not as significant as the one mentioned earlier. Instead of my sword and I have doomed, which follows Masoretic Text, some versions emend the text to read “the sword of the LORD” and “he has doomed” (so Good News Translation, Contemporary English Version, Bible en français courant, Die Bibel im heutigen Deutsch). Hebrew Old Testament Text Project prefers Masoretic Text, but translators may follow the emended text for naturalness since the rest of the section refers to the LORD in the third person.

For the translation of this verse consider the following examples:

• My sword of judgment/punishment has completed its work in the sky;
see, it will fall on the Edomites, the people I have sentenced to death.

• Because my judgment sword has drunk its fill in the sky/heavens,
see, it will now fall in judgment on the Edomites,
the people I have determined should die.

• Indeed, the sword of the LORD appears in the sky.
There it is, falling on the Edomites,
the people whom the LORD has condemned to extermination.

Quoted with permission from Ogden, Graham S. and Sterk, Jan. A Handbook on Isaiah. (UBS Helps for Translators). New York: UBS, 2011. For this and other handbooks for translators see here .