Charles Ellicott Commentary Isaiah 34:5

"For my sword hath drunk its fill in heaven: behold, it shall come down upon Edom, and upon the people of my curse, to judgment." — Isaiah 34:5 (ASV)

My sword shall be bathed in heaven ... —Literally, has drunk to the full. The words find an echo in Deuteronomy 32:41-42, and Jeremiah 46:10. There, however, the sword is soaked, or made drunk with blood. Here it is “bathed in heaven,” and this seems to require a different meaning. We read in Greek poets of the “dippings” by which steel was tempered. May not the “bathing” of Isaiah have a similar significance?

It shall come down upon Idumea ... —Better, for Edom, ... here and in the next verse. No reason can be assigned for this exceptional introduction of the Greek form.